Two different "risks" here

I've personally got the source code for the Nook Color and the Viewsonic Gtablet released, both of which developed vibrant developer communities who, thanks to actually being able to rebase to newer kernels by virtue of having the source, have got newer versions of Android running on the devices than the vendor chose to support.

Availability of kernel source for consumer devices is important, and the uses its been put to are surprising. There are even communities of people who develop replacement firmware for TVs. We've seen what happens without active enforcement of the GPL - most vendors simply never supply their code. Enforcement is a necessary part of giving users the freedoms that the copyright holders intended, and those freedoms make a real difference.