cogadh: No currently available porn site in its right mind will move to the .xxx TLD for just that reason. Why go to a place that automatically limits your potential exposure?
ShmenonPie: Most porn sites are responsible and voluntarily add themselves to filter lists and stuff and encourage adults with kids to install parental safety controls, etc, so I don't think that's as much of a reason as you made out.
However, most porn sites were against the .xxx TLD from the very beginning and still are, for just this very reason. It's one thing to be responsible and add yourself to blacklists and the like that are completely in the control of the user. It's a completely different thing to add yourself to something that, in many cases, is going to be "blanket blocked" long before the user is ever given a choice about it.