If you recall, they brought Quinn in last year and were more than slightly interested in signing him, only to have him choose to sign with the Chiefs instead. This is a pickup, IMO, that makes the most sense as far as bringing in a guy with some experience, who once he learns the system, could fill in if and when he is needed.
Much the same way Clemens was brought in at the end of the 2011 season.
Resigning Davis made the most sense short term, as they at least have someone familiar enough with the system to step right in if we get down to that becoming necessary.
Anyone thinking that they are going to try to do with Quinn, what the Vikings are attempting (and after last night, not very well) with Freeman is most likely going to be disappointed. It is what it is. This is now Kellen Clemens' team.