There is still incentive, just not a ranked number.
To me multi-player seemed awesome, way better than Reach's in the least. I'm think they possibly didn't add it in to reduce the bad-mouthery. Truthfully I don't see where the extra incentive comes from, I mean it's a digital number that means nothing to me outside of Halo, and even then I don't think I would care.
I do feel sad for the respectful part of the competitive community that wanted it though, but I won't feel sad for ones that make demands. I see too many "MLG" players come in and post hateful rants, and I don't like that. Which is half the reason I don't tend to care anymore about being competitive.
My advice, make a public polling petition on Waypoints forums, and try to get something together, but I would advise to keep it peaceful, the more respectful you are, the more likely "343" will listen and try to do something. M$ probly doesn't care.