The vote was 49/51%. Specter outspent Toomey by more than 300%. Specter had the full weight of the Whitehouse actively working on his behalf. You make it sound like he was soundly defeated -- he wasn't. IMO, support from Bush came precisely because they knew Toomey could win.
Ditto.
In addition, the unions were encouraging their members to register as Republicans in order to vote for Specter in the primary.
Does this crossover of Dems and Independents for the primary remind you of someone else???? McCain 2008 comes to mind. I'm getting awfully tired of the Dems and Independents choosing our candidates for us.