No discussion of Shuttle retirement makes sense if you don't mention two important things:
- The Soyuz has always been the vehicle used to rotate crews to the ISS as it has to act as a lifeboat - something the Shuttle can't do with it's 14 day on-orbit endurance.
- Ares I/Orion was supposed to be ready when the expedition crew size went from 2 to 6. It was clear it wasn't going to be, so NASA bought more seats on Soyuz which upped the required production of Soyuz, which increased the average price per seat.
As a result of this framing of The Gap we get people calling for Shuttle extension without explaining how that would solve the lifeboat shortage. I should say, not everyone misunderstands The Gap, I've had discussions with people who suggest such things as buying Soyuz vehicles and launching them in the Shuttle cargo bay as on-orbit backups. It's not a great idea, as the Soyuz only has a 6 month endurance, but it at least recognizes what the real problem is.