Check out the picture of Dickau crashing into the great wall of China in the LA Times. It's hilarious.
This is of course the play that prompted MDsr to get a technical foul. As you can see in the picture, there was plenty of contact, and Yao certainly wasn't set, so it's pretty much a text book foul. But I'm sure the refs were fooled by the simple fact that, from Yao's reaction it seemed there was no contact at all. Usually in a collision of this sort, both bodies react, and the ref is forced to call something. In this case, with the 180 pound Dickau creating contact against the 310 pound Yao, he didn't budge. I think it just threw the refs off.
In the picture it literally looks like Dickau has run into a wall. His face is smashed against Yao like he has hit the side of a building.