"Funny how you all seem to know what the Wii's limits are."
I think we all make educated guesses taking into account what currently is available for the Wii. And in this regard Third-party games until now look pretty similar to the PS2 (often ports but also dedicated games), Nintendo is doing some great stuff but mostly through a cartoonish art style. "Realistic" Nintendo games like Metroid look a bit better than Third-party but not by much.
"Most downgraded ports are rebuit for the system, like RE4"
??? Downgraded portS? RE4 was a Gamecube game so if they had to downgrade anything the situation would be pretty dire. At the moment there are almost NO ports of games that do not also have a PS2 version. So essentially developers do the work twice once for 360/PS3/PC and once for PS2/wii.