Romney wins slightly among independents with each candidate has about 90% support among their own party. To get to the 50-43 Obama lead that means Pew must have assumed a huge (and unwarranted after the 2010 election) lead in the number of Democrats. Garbage in, garbage out.
We don’t have their weighting strategy, but with independents breaking about even, but slightly for Romney, I agree that they are still deciding to see the population with more democrats than republicans.
Rasmussen uses polling to determine their breakdown of dems vs repubs, iirc. Those would be self-reports of party affiliation.
Nonetheless, what this poll says is that Romney is not creaming Obama.
His decision to play rope-a-dope is allowing Obama to define him and define the issues.