I guess because its such a monumental moment, and I think that it can be a mistake to keep him from it. It could be something that he will resent you for for the rest of his life- not that that should be the only reason that you were going to welcome him to it though. And not seeing his child for the first few weeks could upset the bonding that would occur if he was there from the beginning.
But like I have said, its your choice, your birth, your family.
I guess I gave the wrong finger to the wrong man...