I understood that as a marriage ceremony was open to anyone who chooses to just turn up, that there is no reason for the records not to be available. After all the banns are read (at least at the moment, although I know the church authorities are saying this is out of date) so that anyone can find out who is getting married and make an objection if necessary.
I agree with divorce records not being on line, but I don't see what the problem is with baptism records. I guess it's just a money making exercise for the Dioceses who hold them.