IMHO, Nike cutting ties is real linchpin move that sends Watson south from here on out. Imagine the investigative team they can assemble and turn loose to investigate one of their athletes. If they thought they should give him the benefit of the doubt - and with the extreme racial tensions existing everywhere - they undoubtedly would have.
But the out-and-out "bye-bye" means they dug into it, realized there's plenty of fire behind the smoke, and wanted to disassociate ASAP.
As others have said, when you go from saying nothing happened at all to "well yes, we did some sexing but it was totally consensual", it's all over but the crying. Despite all the wink wink, nod nod stuff we know exists at certain massage parlors and with buying massages off the Internet, you're still taking someone's legit profession and deciding you get to dictate it becoming a sexual encounter. The ritualistic behavior that we get from story after story from the women complaining is the sure sign of an addict, and someone who is desiring power over other people in interactions. He should check into rehab ala Tiger and look like he's trying to get better and admitting this is a problem, will probably make it a lot easier on himself in the long run.