That doesn't really "prove" anything.
Motostorm has got a long way to go to match the E3 trailer.
However in it's own right I think it's still impressive - especially the mud physics, the buggy and bike models, motion blur and lighting (seen in the better quality GDC videos).
The weak areas were the barren environments and poor textures - although Harrison said the game had been stripped back just to show off the mud physics so we'll have to wait till E3 to see the progression of the game.
I found the videos very encouraging - it seems the meat of the E3 trailer is there - they just need to add the frills and bring it all together - let's hope they can manage that over the coming months.