I know Yao hit that incredible shot to give Houston the lead but what in the blue hell was he doing on defense?

What the hell are you talking about? That was a great play by Roy, but that is still a one in a million play. None of those guys wanted to get called on a foul on Roy, so they probably figured in the thick of the moment to not try to stick a big hand in the face of a guy shooting a fadeaway 30 ft. jumper. It was a good shot, but there is nothing that they could have done on that play.