It appears that Romney, and Romney alone, was the driving force behind the selection of Ryan.  From Buzzfeed: 

“Everybody was against [Ryan] to start with only Romney for,” said one top Republican, who is skeptical of the choice and griped that Romney’s top advisors have “been giving Mitt everything he wanted in this campaign.”

Many of the concerns are based on the exact reasons why many Dems have been ecstatic over the selection.

Some of the doubters, though, also see warning signals. Congressional candidates in difficult districts and Florida Republicans are not eager to debate Ryan’s attachment to converting Medicare into a system of vouchers for workers under 55. The fact that Ryan’s push to cut capital gains taxes, which Romney opposes, would reduce the presidential nominees own taxes to nothing has also gotten unwelcome attention.

I’m guessing that this will be the first of many articles detailing how Romney’s staff was against the pick, particularly if Mitt’s poll numbers stick after whatever bounce he may, or may not, receive from the selection.  The move from Romney’s staff to stick him with ownership of the selection is clearly designed to ensure that if Ryan craters his staff will be able to have their “I told you so” moments to ensure maximum employability after an Obama victory.  Campaign consultants, after all, need to eat.