A fair point to mull over, but here's where it falls apart.
Democrats like both Hillary Clinton and Barack Obama. They always have, they're both exceedingly popular within the party, always have been. Democrats had two good candidates in 2008 and struggled a while to figure out which they liked best. They ultimately chose Obama, and he won in a minor landslide.
By contrast, Republicans do not like Mitt Romney. That's why we see half or more of GOP voters lurch from:
Sarah Palin
to
Donald Trump
to
Michelle Bachman
to
Rick Perry
to
Herman Cain
to
Newt Gingrich
to
Rick Santorum
We're talking about a huge pile of GOP voters looking for someone, ANYONE, who isn't Mitt Romney. They just don't like him, they don't believe he's one of them (I think they're right).

Mitt Romney is vigorously supported by former Minnesota Governor Tim Pawlenty. With Pawlenty's support, Romney came in a distant
third in Minnesota last night. He lost every single county!
By and large, Republicans do not like their nominee, Mitt Romney. We'll see if that means he loses this fall, but it's a real big problem for his prospects.