"So on the Wii you would have a graphical asset model and textures while rendering the game at 480p with 2xAA; on the PS3/XBox 360 you would have a similar model that had 2 to 4 times as many polygons, 2 to 4 times the texture detail, high level pixel shader effects, while rendering the game at 1080i/720p with 8xAA and 16xAF. The XBox 360 and PS3 game would look far better but the core gameplay would be identical on all systems."
That fact is i think the majority of developers will be "lazy" enough for things happening this way.
But effects and calculations will be doable on Xbox360 (parallel computing capable) and even better on PS3 (distributed parallel computing capable, as said by Kars, in which he is perfectly correct) that you won't be able to do on Wii.
Will that change the paradygm on presentation for the games ? If i had to give an answer now, my answer would be NO. Because, IMO, the next shift will be when raytracing will be acheivable real-time. Raytracing will not be possible before next-gen (PS4 and Xbox720), and even at this moment it is actually questionnable ...
edit : changed "raycasting" to "raytracing" after Harry's comment ...
