Tachometers - Why do they still exist in most automatic cars?

Allow me to preface this by saying that my first two cars were manual transmission.  Allow me to add that my dad taught me to drive manual on a 1995 Chevy Cavalier with no Tachometer and only a Shift Light (or an idiot light as my parents referred to it).  As such, I was taught to shift based on the sound of the engine and feel of the car.  This went the same for my first car which was a 1986 Ford Escort Wagon with a four-speed manual transmission and a broken Tachometer. 

Moving on to the real point of my post, why are most cars Gauge Clusters wasting space with a huge Tachometer still?  On average, I can only see it being useful to a mechanic trying to diagnose a problem with a car, but the average driver never even looks at it.  For the past four years I drive a GMC Sierra pick-up truck and I never looked at the Tachometer on purpose.  I also drove a Volkswagen Beetle for work (I'll let you guys speculate who my employer was and laugh about it) for about two years and never had a need for that one either.

That brings me to my new car I purchased last week, a shiny new 2011 Subaru Outback.  I wanted the six-cylinder engine, so I was forced to get the automatic, but the dashboard is the same on all of them.  From left to right you have four gauges: eco-fuel economy gauge (which I'll rant about in another post), the tachometer, the speedometer and the fuel gauge. 

 What I would like to have is a temperature gauge so I can see that my engine is getting warm or about to over heat rather than wait for the red temperature icon to come on (you can see it in blue in the eco gauge).  I suppose we could bring back the oil pressure gauge or battery gauge too.  While most people won't know exactly what they represent, hopefully they'll at least recognize that red equals bad and you should get your car looked at.  They could also move the outside temperature, miles in tank remaining, and clock from the center area of my dashboard in front of me. 

Another great alternative would be to get rid of the Gauge Cluster altogether and have a larger windshield with just a Heads-Up Display (HUD).  My father-in-law used to have a Pontiac Grand Prix that had a HUD that projected everything you needed to know right on the windshield.  This let you watch the road while monitoring your speed, radio/cd info and even warning messages.  I thought it was a great addition, too bad it couldn't keep Pontiac alive.

Of course manual transmission cars have a need to keep the Tachometer, as well as anyone who might be towing a trailer or other heavy load so they can monitor there need to shift into lower gears on hills and downgrades.  But what about the 80% (made up, but possibly near accurate statistic) of vehicles out there that are wasting space with such a huge gauge.  Do we keep them just because that's what we've always done?  I'm sure car manufacturers can come up with something useful (or equally useless) to take up that space.    

I don't know much about cars, but wouldn't a HUD be expensive as hell?

It is pretty pointless in automatics. It is nice to know how "hard" your car is revving, but it's far from necessary in most cases. I'd be happy if they could just shrink it down by 80% and stick it in a less conspicuous spot.

I have that HUD on my Grand Prix.  It's incredibly convenient, but it's not a big fancy HUD that most people are expecting.  Basically, it's an old-style LED (think: alarm clock) screen mounted on the dash pointed at the windshield.  It reflects back the image so that it appears to be floating in your field of view.  It does have decent information: speed, radio station/CD track number (if you change the station/track/volume), and a couple of warning lights.  I disagree with putting too much information in front of your field of view, too much would be distracting.  If you could pick and choose the info you want, that'd be cool, but it would be expensive to develop.
The tach is good information for me, and I have an automatic; my car is pretty quiet, so I can't always hear how hard the engine is running.   It will give an indication that you're pushing the engine too far.  This is especially useful to me since I have a turbocharger.  It will also give me an indication that the transmission is starting to go based on when it shifts.
Most cars (read: every one I've ever driven) have a temperature gauge.  Maybe it's a local thing, like mandatory block heaters (you can not buy a car without a block heater where I live, unless you special order one without), but I've never seen a vehicle without a temperature gauge. 

it is a good question. i look at mine all the time to know where my car revs and things. acura TL have a lot of information on their dashboards. they have percent on how the oil is doing, tire pressure, and other cool stuff. 
 
i think they do it to save money. when they have to make an automatic and manual they don't have to do anything to the automatic one.

Because it is often easy to switch to over drive and 2nd drive and such without knowing it and the tachometer will let you know if your engine is at an RPM it shouldn't be at.

" Because it is often easy to switch to over drive and 2nd drive and such without knowing it and the tachometer will let you know if your engine is at an RPM it shouldn't be at. "

What it comes down to is cost.  It is alot cheaper to use one mold for the cluster then to make two different ones.  Also it does have added use even in an automatic.  
     Imagine some grandma gets into her car and puts in into 3rd instead of drive(or second depending on your shifter)  Now most older people really dont pay attention to their cars sound let alone revs.  So when shes driving down the road and hitting the rev limiter instead of just stoping and calling a tow company cuz her car is "broken" she might actually see that little rpm needle pegging off the revlimiter and realize its in the wrong gear. 

      ALso other ppl hit good points too, like knowing how your tranny is performing, also if your idle raises from like 800 rpm to 1100 or 1200rpm it could be time for a tune up or a sign that something is drawing more power than it should but that is more for ppl mechanically inclined than your normal everyday drivers of automatics.  
       BTW nice ride too bad they didnt offer the 6 cyl with the manual.  u should have splurged and went with the STI :)

I'm not so much trying to complain as making the observation and almost playing Devil's Advocate.  As we dumb everything down for people more and more every year, I'm just surprised that the Tachometer hasn't gone completely to the wayside.  And as stated before, their are dashboards without a Tachometer, so the argument that it's cheaper to produce one dashboard could go to either side.

I think the tach is still plenty useful to have, but I think that it should probably be smaller and allow for (like the TC said) a temp gauge or a battery gauge.  I drive a stickshift so the tach is a must, obviously.

Well, i was taught to drive car like you on a manual by engine sound. I think its just for show, since i see no point if it in an auto.

I learned to drive manual without the tach just by the speed and engine sound like some of you have said. Too bad that car is gone I want another manual car. -_-