I say it was poetic justice, and Ortiz looked like an amateur in the ring. You NEVER take your eyes off your opponent with your hands down especially after you blatantly headbutt him because you're frustrated that he's slipping more than half of your punches. Mayweather was going to comfortably win the match, but I'm sure he wasn't intending for it to go down like that. He was landing a higher percentage of his shots and he had more ring control against an aggressive power puncher. I say it was justified. That headbutt could have caused Mayweather not be able to finish the match. The cut lip could have been very serious.
P.S. and lets not act like there haven't been "cheap shots" immediately after glove touches in MMA. I can name a few accounts where there have been blatant cheap shots in MMA.