Here is what I don't understand. Just because we don't have to worry about THEIR center doesn't mean we wouldn't gain an advantage by having them worry about OUR center (which they currently do not).
Shaw is no longer a great low post scorer. Decent, but not great. BUT, teams absolutely know that they can't leave him because he will still finish around the rim. He is a huge target with great hands.
Shaq's presence would make guys like Anthony more hesistant to go blocks because Shaq would be open for passes (i.e., lobs) under the basket or would grab offensive boards.
I agree, this is where Shaq's value is. He doesn't give us a lot on defense beyond 6 fouls, because he simply is not quick enough to make the rotations. However, offensively, he absolutely makes an impact, and makes it significantly easier for the C's to score against this defense.
I still think though, that he is not a necessity. He would help, but if this team is absolutely good enough to beat this Heat team without him. They just need to clean some things up, and execute better, and they should be fine. But he would certainly give them a larger margin of error.