First off, NO, 360's graphics are certainly not better. Try the game Uncharted out for PS3, will blow away anything you've imagined on 360. The cross console games at this point have been more ports from 360 to PS3, those that were made individually are even or given a slight edge to PS3, those ported to PS3 from 360 however 360 stomped PS3 which is why some people believe 360 has better graphics. At this point though, it is really just a toss up but in the long run PS3 has far more potential.
The reason Wii has sold more is A. Cost efficteveness and B. Innovativeness. That said, PS3 and 360 have pulled in more money because they need to sell less to make what Wii does with a couple sales. The majority of Wii's sales were in the beginning, now they hardly ever sell(ask any local store). Everyone who wanted one already bought one and now the games they've been releasing as of late and for the next year are all either cross console or they suck. And why would you buy a game that has worse graphics on the Wii when you could get it on 360 or PS3? Besides which, anything difficult is much easier to play on PS3 or 360. While the controls are fun for some games, it makes challenging games almost impossible.
I'll add more if i have a chance later. BTW the guy who posted nintendo power ratings should have picked a different place, of course nintendo will rate their games far better than somewhere that isn't biased towards their own games, try Gamespot or IGN.