With a market bereft of reasonable starting pitching deals, the Red Sox did not have many options. The price for Ubaldo Jimenez was prohibitive (especially for a team that is just now rebuilding its minor league system after the Adrian Gonzalez trade), Hiroki Kuroda's no-trade clause kept the Sox out of the mix for the Japanese starter, Wandy Rodriguez and Doug Fister, and the Rich Harden trade fell through thanks to poor medicals.
That left just one pitcher available with the potential to really contribute to the team as the playoffs approach: Erik Bedard. His terrible return game was enough to bring down his price to the point where the Sox would only have to put up third-tier prospects like Federowicz, Chiang, Rodriguez, and FIfe--none of whom really threatened to factor into the team's long-term plans--while his longer track history speaks of a starter who can be dominant while he's healthy.
The Sox would have preferred more of a sure thing, even if they weren't a top-flight starter. But the reality of the situation was that the only options out there were risks and top-tier starters that would bankrupt the system even further, and even they had lingering questions. Bedard is something of a less-extreme version of Rich Harden, who did have 15 straight starts before missing most of July.
To be certain, Bedard's start against the Rays was concerning, but he had a 3.00 ERA when he went on the disabled list to begin with. Presumably the Sox will be satisfied that his medicals show he's recovered from his most recent injury before the trade goes final. If that turns out to be the case, then the Sox will have a chance at having acquired a front-line pitcher. With only Jon Lester and Josh Beckett sure things in the rotation this year, they needed at least one more man that wouldn't be embarassing to start in the playoffs.