One thing I forgot to add, many HDTVs will remember settings for different inputs, independent of other inputs. If you're going to compare the two input ports, you have to make sure that both have the same menu settings; you can't just plug them in and take your pictures and go "a-ha, they are kinda different!"; duh, they were different before you plugged anything in. I doubt any of the "reviewers" remembered to calibrate.
I see no difference in clarity. The darker images look oversaturated, maybe due to the converter's crazy opinion on color settings; oversaturation is a bad thing in the feed because it destroys native texture details, like other "extreme" settings do: in contrast, brightness, etc.
At best, here 1080p describes the signal, or the potential of the video feed. The Wii source content it's trying to translate hardly reaches this potential. Take your 0.3 MP webcam image and resize it to 5.0 MP -- not too hot.
The rule of thumb for video conversion is: "trash in, trash out"