The click on quick reply thingie is for the threaded/hybrid mode, otherwise vbulletin doesn't know what thread you are replying to and kinda screws things up.
I could make it default to the first post id with not much trouble (it's a vB3 option) but that would make hybrid and threaded mode not make much sense, since nobody will want to click on the post they're replying to unless they're going to quote it.