You're missing the point.
After Brown won in MA, many in the GOP touted that they would win this one too, especially since the election was taking place after the health care bill passed.
In fact, the GOP candidate specifically said as much, claiming that this election was a referendum on the health care bill.
You can be sure had he won, the GOP candidate would have screamed that his winning was because of it.
You can't make such a claim and then, after it's over, make excuses as if you had never said such a thing. It's not a referendum on health care only if you win.