Greg doesn't have the arm to be a regular starter in the NFL. I consider that a settled matter. He is, however, an accurate and extremely intelligent player who developed well and over-achieved in college.
With Sanchez a basket case, and Tebow having no business being a starting NFL QB, Greg is the best choice. It's probably the first rational decision Ryan has made this season. My question is whether he deactivates Sanchez so he can keep six WR. THAT would be a statement.
As has been mentioned, I think Greg realizes his role is to not screw things up. I hope he has a good game and the Jets win 20-13.