Williamson also said he didn't see it likely that the community could keep up with maintaining open source drivers without the cooperation of the hardware manufacturers. The device updates tend to move so quickly, and the skills required to develop and maintain the drivers without assistance, make it unlikely that the community would be able to maintain a 100% free Android system with drivers. Of course, Linux developers, who have managed to keep up with a lot of fast-changing hardware over the years, might just disagree.
The difference being is that PC hardware tends to live longer than phone hardware. A phone may only be in production for 6-18 months and the chips in it may not stay the same through the entire run. Then the lifetime of a phone for many people is 1-2 years at most. So by the time you have a driver, your phone is no longer sold, most people aren't using it, AND you can't be sure the driver will work for all of that model phone.
It takes the hardness of supporting Laptops due to constantly changing specs and increases it quite a bit. It is not an impossible task but I can see where it would be a lot more draining that dealing with even nVidia cards.