Well, back when the PS2 version came out and offered a 'proper' widescreen mode, I compared what was being output there, to outputting the game letterboxed and using the zoom function of my TV and found there was no difference.
When the Wii version came out I checked again, and found the same thing. When they got it working on Dolphin I did some screenshot comparisons to see what happened with the internal scaling.
If you run the game on Dolphin in 4:3 at 1280 x 960 (a 4:3 resolution) what you get should look identical to running the game in 16:9 at 1280 x 720, just with black borders top and bottom, but cropping the 1280 x 960 shot and comparing it to the 720p shot, the 720p version looked notably worse.
or you can just do the whole pixel counting thing. but that's how I found out anyways.