Dead Rising 2: Case Zero, What Demos SHOULD Do

(Note: Typically I would be writing this on my personal blog, but I think I'll be keeping it here.  I really am hoping to stretch my writing bones with this.  Also remember this is solely OPINION.  I'm very interested to see what others will think.) 
Last week Dead Rising 2: Case Zero came out exclusively to XBLA to what seemed to be universal approval (79 is good enough for approval right?).  Anyway this was Capcom's experiment with something new, how would a payable standalone demo work out?  Of course they were aiming for players to buy this demo, like it, then go out and buy DR2 when it comes out.  But they also risked facing people complaining that they had to PAY for a demo or even worse that this demo did such an excellent job that people WOULDN'T BUY the full game because it would be more of the same of the payable demo.  A week later the experiment seems to have worked (being sold 300k times in the US alone for a total of about $1.5 million) for right now, but it'll be a couple of weeks before we see whether or not this was truly successful.  Whether or not this is a success isn't really the topic, but rather what I'd like to talk about is what this game did RIGHT as a demo and if anything can be LEARNED from this experiment. 
To me the point of a demo is to not only show the player how the game works but rather try and to get people to actually BUY the game.  To my knowledge I don't think there have been demos that have gone outside of the game's story (if I'm wrong point it out to me), therefore "spoiling" the beginning of the game for those who've played the demo.  This isn't really a problem for many people, but for many gamers who play games for the story (such as me, and rather silly as many people have told me) this beginning can ultimately make or break the game in their eyes.  A demo is kinda like reading the first five pages of a book, if you don't hook us in it's going back on the shelf to only be bought when it's marked down or used.  Even if everything beyond what the demo showed in the full game is one of the best games ever, that doesn't get over the fact that the demo FAILED to do it's job.  In DR2: CZ, we don't get the beginning of the full game, we get a prologue.  A short story with a full beginning, middle, and (multiple) ending(s).  It doesn't spoil, rather it shows me the events leading up to the full game.  To me this demo accomplished both goals completely.  I am excited about this game now (before I was on the fence since I didn't really like Dead Rising 1 all that much) and it made me put in a pre-order for the game. 
The major lesson we can all walk away with from the CZ experiment is: DEMOS AREN'T JUST PREVIEWS.  I'm not saying do a throwaway story or prologue for the full game as a demo.  What I'm saying is, if a developer/publisher is willing to take the time to craft a demo that can work as a short companion piece to the main game, then it also shows the customer that if something this short was tended to.  Odds are the full experience will be just as or even better.  Taking your time to craft an excellent demo can ultimately swing a person to buy the product, which is what demos are supposed to do.  Also the fact that I can carry my level, skills, combo cards, and (hopefully) money from CZ into the real game gives even more incentive to replay this demo over and over again to prep myself for the full game.  Demos can be previews, but what CZ has shown is that demos can be a whole lot more if given the chance. 
I hope to see more stuff like this in the coming years...granted CZ isn't perfect but it's certainly a major leap in the right direction.