Frustration at Primary without knowing complete "ticket."

Am I the only voter that is annoyed to vote at the Primary, because I don't know the complete ticket if my candidate wins? While I voted for McCain, I don't know if I could vote for him in the General Election if by some quirk he takes on a running mate that I have a strong negative opinion. I believe this feeling is showing itself (to me), since with the current administration, I thought, the Office of the Vice President seems to have had an apparent significant involvement with certain concerns. More so, perhaps, than many past Vice Presidents? So, why don't we have a complete ticket to vote for at the Primaries? Would it be that hard for candidates to at least give a list of their potential running mates? It's as though the Office of the Vice President has evolved to a more meaningful position. Shouldn't we therefore have the ability to vote on who will be in this office?