I'm guessing they went so hard after hitting for a few reasons:
-For better or worse, more long-term money already tied up in Pitching (4 starters locked in for a few more years if you count Bucholtz's arbitration) while Drew, Ortiz, Beltre, and Cameron all either come off the books after 2011 or are off now.
-They probably expect that even though they were 2nd in offense last year, and they'll be getting Pedroia/Youk/Cameron back for hopefully mostly the full year, a lot of offense last year was due to the ridiculously productive Beltre, a year they probably think is an outlier. Combine that with what I think they think will be continued decline of Drew, questions of ellsbury, and decline of Ortiz, and I can see why they wanted to upgrade the offense with non-Beltre players. Plus...
-I'm sure they expect some improvement from Bard, some return to form of Beckett/Lackey, and hopefully some return to form of Papelbon. This would internally improver their pitching rather than adding more long term money to old pitchers via free agency, say if they had gone for Lee over Crawford.