the 76%-80% of americans (depending on the poll) who supported the repeal of DADT had very little effect on the majority of the GOP'ers, who were so obsessed with culture waring that they didnt care that a unheard of majority supported repeal... it could be 90%, and the GOP will still fight against the right of gay people.
51% is not a lot, but the trend is obvious, however, the pro-discrimination base comes out strong, as shown in Maine in the last election. I think this issue will still help gop candidates in many areas get elected for another ten years at least. It's always been an issue to raise money and they'll milk it dry.