They actually completely stopped development on IE between version 6 and 7. There was no IE dev team, beyond people patching bugs.
Obviously this did not prevent other people doing GPU-acceleration, but the leading player deliberately halting development will and did cause the market to stagnate.
That's not really relevant to the issue at hand, though. Bringing up Microsoft's misbehavior with IE 6 in this context is like bringing up the time a kid cut in front of you for lunch in third grade when you meet him in college.
Obviously this did not prevent other people doing GPU-acceleration, but the leading player deliberately halting development will and did cause the market to stagnate.