You don't understand how slow mobile chips are. You have no idea, ATI 32MB M4 or not. BECAUSE they are notebook chipsets, they are limited by bandwidth, they are limited by power and they are limited in almost every performance related way.
When you have to redraw the desktop at say 1400x1200 you should see it on some current "high performance" notebooks, it's just so slow.
So it's not about 3D, it's about how fast the chip is overall, and perhaps Nvidia will bring something new to the market!