Originally Posted by Superdude
Just because we've had some good luck doesn't mean all starting pitching prospects pan out and flood your rotation. It pays to have as many rolls of the dice as possible. And starters are simultaneously capable of pitching in the bullpen. If you can keep both options available, the only reason to eliminate starting is to fast track someone, which unless you have a good reason for it, is shortsighted most the time.
Just read through the May 31 MLB.com article on relief pitching. It explains why teams are beginning guys as relievers earlier. Among other things, it makes economic sense to sign relievers early, move them up quickly, and control them as major leaguers for several years.