I have a friend who works at a high profile tech company whose main job is to ensure that they stay within the bounds. It's a highly technical, constantly evolving field of law. As I understand it, the case law on the various IP issues related to the GPL are still quite murky (i.e., there hasn't been clear and convincing precedent established yet by SCOTUS or even the courts of appeal). There is a legal theory that any and all works that are derivative of anything under a GPL is subject to the GPL, but that isn't the only one or even the predominant one.

My guess would be that whatever enTourage is doing is within some mainstream interpretation of the GPL. If you think otherwise, then you're welcome to sue (seriously, that's the only way to try to enforce a particular interpretation of the GPL). Strictly speaking as an eDGe user, I'd prefer that you didn't so that they can stay focused on serving us a fresh batch of Froyo later this summer (and they generally seem like nice folks).

Hopefully the forthcoming SDK will help people develop their own enhancements for the eDGe.