This connects so many pieces.
Apple has repeatedly stated their apprehension about the netbook market being that it is impossible to make a system with a solid user experience at the $500 price point (think about it, that's the cost of an iPhone without contract). But by putting a 2 year contract for 3G services, with say AT&T, would open up the opportunity for a hefty subsidy (similar to with cell phones) on a $700-$1000 system and hit the price point that the market demands. This would also give users a more complete always-connected mobile experience.
I see this happening before 2009 ends.