Indeed they could, I just said that. This lock might force MS to make IE's engine as good as WebKit. I don't see any problem as long as the standards are kept open and the engine doesn't belong to a single entity.
You got the lock-in strategy backwards. It exists to allow the incumbent not to improve their products while maximizing their profits because they don't have to compete.
That's how IE6 used to be, too. But because they eliminated all their competition, they didn't have to advance it anymore. It was cheaper and easier to keep it the same.
