The NCAA feels that off-field violations are WORSE than on-field ones. On-field can be described as "emotion" or "heat of the moment". Off-field stuff is "premeditated". I'm not agreeing with that, but from what we have seen, thats been their M.O.
Lets also face the fact the NCAA is fighting off a ton of black-eyes right now (Penn State, Ohio State, Cam Newton, Reggie Bush, etc). They have tried letting schools handle discipline issue themselves, and it NEVER works.
I don't know how I feel about it. Part of me thinks that this should be handled by the school, but I know any "off-field" things handled by a school will disappear without legitimate punishment.