This is part of it, yes, but there are a small # of Democrats (myself included) who vote Democrat for other reasons. I abhor the plethora of positions the Democrats take on most social issues, but I see no practical effect of voting them in on, say, abortion. Take Obama, for instance. He has a very, VERY radical pro-abortion history, but he doesn’t even attempt to push abortion legislation. Even when his party had 60% of the House, the House was almost 2/3rds pro-life. On the flip side, I have seen no interest in Republicans taking any kind of active pro-life stance; they vote for pro-life bills in secret and use them for fundraising (see virtually every single one passed this year), then they turn around and only talk about economic issues. (The same is true for same-sex ‘marriage;’ look at all the Republicans running away from their religion in the name of politics). In addition, two Republicans with heavy pro-abortion histories have been the last two presidential candidates, effectively neutralizing the argument for me.
Secondarily, I support the traditional Democratic argument to international relations and war (although Obama has been a strong continuation of Republican policies in that regard, irritating me). I also support the Democratic argument on many economic issues (e.g. the benefit of having unions), voting rights, and the death penalty, to name a few other issues.
There is more to it, but I figure if you care to know, you’ll ask. I am not closed off to voting for Republicans certainly, but I will not vote for a severely sketchy one just to keep a pro-abortioner out of office, for the above reason that they will be heavily neutralized in any attempt to do anything about it. Long story short: Do I like Obama? Not really; in fact, I think many of his actions are quite bigoted or abhorrent. Do I like Obama over Mitt Romney? Absolutely.