All systems have their finite resources, how devs choose to use them is not dependend on the power of the system. You will have games that try to push the Wii to its edge with flashy graphics, and games that focus on gameplay - its the same for any system to date.
So the question is rather how do the games compare to other systems (not only graphically) ? If you have more resources you can realise more (or the same easier), so its not looking to bright for Wii IMHO.
I think on any given platforms there are simply levels of graphics fidelity consumers are willing to accept.
DS games go for 40€ around here and, as a rule, look like DS games. Bring out a DS game, with the exact same graphics and the exact same price, on any home console and consumers will break out in tears, magazines will tear you to shreds and the internet will hate you.
Some XBox Live Arcade games look to be on
that level, but then their prices are very low, and probably for a reason.
In principle I agree with you, platform boundaries are artificial, and simple, focused games could be anywhere. But it seems publishers are reluctant to bring out fugly games for the more powerful platforms in practice. I don't know if I can explain exactly why this is, I probably can't, I just know that I don't see many games going against the grain.
Meanwhile on the perpetually underpowered Nintendo handhelds those ultra-high-risk things with fugly graphics are in fact happening.
http://en.wikipedia.org/wiki/WarioWare,_Inc.:_Mega_Microgame$
http://en.wikipedia.org/wiki/Rhythm_Heaven
http://en.wikipedia.org/wiki/Electroplankton
(needless to say, some of them are highly obscure and/or tank commercially, but they at least exist!)
