In 2004 Kerry won PA by a small margin-- by 143,000 votes-- BUT dems did not have a 1.1 million registered voter advantage.
PA in 2008:
Registered Dems: 4,060,647
Registered GOP: 2,917,747
Registered Indepedents: 869,707
PA in 2004:
Kerry: 2,938,095 (registered dems: 3.9 million)
Bush: 2,793,847 (registered gop: 3.4 million)
Statewide average voter turnout: 62%
For McCain to win PA he'd have to get ALL the independents AND over 20% of registered dems. Voting turnout is expected to be high, Allegheny County (Pittsburgh) alone is predicting an 85% turnout. Between 2004 and 2008 dems gained 500,000 registered votes and the GOP lost 200,000 voters.
So we'll see what actually happens on November 4th, although there are over a million reasons in PA alone to be pretty optimistic.