why the 2gb ram limit on laptops?

[Robo]

It makes no sense given that 2GB was the minimum amount of memory to make 10.4 usable (or at least a pleasure to use) on powerPC macs. With Rosetta, and some macs like the Mini and MacBook having shared memory for VRAM, 3GB is probably the new minimum. The new 512MB Mini in our household is actually slower than the old G3 600Mhz iBook that has 640MB when it comes to launching powerPC apps or having multiple apps open.