The pipe industry has been dealing with 10,000 psi pipe and flanges since 1949. Don’t let the BP people pull a fast one on you.
http://www.woodcousa.com/flange_history.htm
It has been thoroughly documented that BP has screwed this operation up. They were totally unprepared for any failures or disasters. And they told the government they WERE prepared and had to file documentation as to what they would do.
BP needs to be explaining why this fix was not started on Day 1.
But the problem of trying to cap a high-pressure stream like that, under that much water, is not remotely trivial.
It's not the same as drilling a clean well -- it's like trying to screw a cap onto an operational firehose .... times 27.