Did you catch Jon Stewart's parody of that issue? It seems Romney was appalled that Democrats would do such a thing, it was a terrible strategy, and so on, but then Stewart ran clips of Romney supporting the Republicans having done the exact same thing back in '08, cheered on by, you guessed it, the same Romney.
Political gamesmanship at its finest.
Romney condemned Santorum for calling on democrats to crossover. Obviously the practice is widely used as a strategy of the opposition. I do not recall opponents using the practice before (does not mean its never happened of course). So not the exact same thing. Perhaps that's why its a parody ?