Hi guys, 
 So im planning to get Civ V tomorrow and i know you need Steam to play the game, I already have Steam so thats no probs. What i need to know is why exactly do you need Steam? I live in Australia and i have shitty internet speed and download limit, the Steam thing isnt an actual download of the game right (like it would be if i had bought if from Steam itself)? Its just some form of authorisation or something?  
Just wanted to clarify all that before i head out and pay $70-80 for it tomorrow coz if i do need to download it im going to be in trouble with my download limit. 
Thanks.    
 
EDIT: So i got home with the game about an hour ago and installed it, it was all done on the disk, no downloading needed, Steam was just for the authorization after all. WOO! 

If you have a retail version, you should be able to install off of the disk.  Steam allows you to have games saved to the Steam cloud in case, for whatever reason, you wanted to continue a game on a different system.

You'll most probably be able to install it from the disc, steam is just for authentication.

Steam provides achievements too, but mainly its the game's DRM.

Ya, you install it from the DVD's but it has to connect to your Steam account to add the game to it. As mentioned, it's just a way for them to patch the game more easily and there choice of DRM.

Here's a question my friend is trying to figure out:
 
If you buy a Civ V retail box, and register it with Steam as you need to do.  Will you then be able to later install the game on another computer through Steam or do you need the retail CD still?

I can't optimise my pc with steam, it sucks because I could increase the performance of my computer but it fucking won't let me, 
 
 
boo. 
 
and it crashes a few times...