There are several effective arguments to be made, that the NFL needs a developmental league, somewhere along the lines of what the NBA has with their D-League.
We can make an effective argument beyond the fact that two 2010 draft eligible QB's (Tim Tebow, and Mike Kafka) may have their career derailed, because these is no such league in place.
There is nowhere for them to hone their skills, beyond the UFL. However, there are several business related issues that prove the NFL needs a D League of their own.