To be honest, I was asking the same question.
I quickly discovered though you can't really do a straight up comparison between ps3/wii.
All the effort on the wii has been put into the movement functions. The actual games & software are secondary to this. Hence all the games I've seen so far on a wii have been dodgy looking "cartoon" graphics.
Even their flagship "wii sports" hasn't got enough space to have figures running about the screen with legs, they just hover around the screen.
As has been said already, the wii is a social console. But if you played it by yourself, it would bore you within the hour. The software is aimed purely at this level so you will never get the breathtaking graphics you get on a ps3.
The Ps3 on the other hand ( yes jamie i'm a sony gaydo
) can be both. you have the motion sense controllers & you have the network play/ 2 player setups. But you also have the "bloody hell" graphics of the software & the sheer versatility of the console. When you buy a ps3 game, the first time you play it, it updates to the most recent software version to repair known glitches etc.
Plus a little known fact is that a dual layer dvd has about 7-8 GB on it. A Ps3 blueray disc has about 60GB on it.
Go sony m8, you know ya wanna 
PS
Ask any ps3 owner about the joy of Call of duty 4 online. Its playing soldiers for grown ups - well big kids anyway 
They are aimed at different markets. Actually, the PS3 is an oddity, as its not entirely aimed at gamers in a sense - it has another motive, related to Sony's survival.
Sony wasn't looking too healthy (still isn't), and had pretty much bet the company on Bluray, which wasn't going too well against HD-DVD. In order to win the battle, Sony used the PS3, which they knew would sell due to PS1/2 sales (and Sony customers are stupidly loyal), to get as many BR players out there
that they could control (as Sony, in typical fashion, kept changing the specs, many early BR players will no longer play newer titles). Sort of similar to Microsoft's alledged underhand tactics, only people don't hate Sony as much.
This is why PS3 was also rushed and released when not ready, and also why sold at a loss. Not to mention why they didn't have the ability to get the PS2 emulator working properly, before quietly
changing the specs in true Sony style when they can't get something to work dropping it.
The problems with the PS3 and the need to get it out early are the reason why the PS4 is rumoured to be out in 2010.
As to the disk capacity for games, it will be similar to when games first came out on CD, and then DVD - the extra space won't be used for the game, but will be used for intros and videos - which is very nice if you buy games to watch such things. I'm sure the space will get used at some point, but not quickly, for 2 reasons - portability between other platforms (Xbox and PC still predominently DVD), and the fact that coders are still struggling to get to grips with the PS3.
As to online game updates, virtually all games across the main platforms do that anyway. Good on Sony being able to do this at last
