I think they'll have similar opening weeks.
As for LTD, I think it could also be similar - on the one hand, L4D2 seems to me a little too much of an "update" a la yearly updates of Madden, FIFA, etc, but then on the other hand Uncharted 2 probably won't get anywhere near as much bundling as the first.
So, I'll say close for both week 1 and lifetime. My place on the fence is quite comfy!