The Burnout 3 claim was made by a developer in this very forum years ago so you'll have to search (Basically Burnout 2's particles, AI and physics systems were updated so much for Burnout 3 that GC's CPU couldn't handle it)
In regard to multiplats this shocked me as I always thought GC was easily between PS2 and Xbox (But closer to Xbox)
But the reality is there are many mutiplats where GC offers higher resolutions over PS2 but can have some pretty big cut backs in visuals and a lower frame rate than PS2.
This video shows it perfectly, graphically PS2 seems to doing everything effect wise that Xbox is doing (Just at a lower resolution)
Where as GC is the same resolution as Xbox but offers cut back visuals (No DOF, motion blur, bloom...etc...etc...)
And this isn't a one off either, the more video's you watch about GC vs PS2 in multiplats the more you see it wasn't as clear cut as people always thought (me included)
(This is a good channel too as some of the differences between PS2/Xbox/GC are fascinating)
The driving section later on in the video is especially poor on GC.
Now for a machine released later than PS2 it's not a good look.