Tyson was still Tyson after Buster beat him and generated big numbers post prison.
Even after his loss to Evander, he was still on. People still believed that he would come out in the rematch and break bones on Evander inside of 2-3 rounds (instead of Evanders bones, he went after his ear).
And even 2002, when he was totally shot, a lot people had that image of Tyson knocking out Lennox.. they still believed the guy from 1988 was there.
With Floyd, whose style isn't as nearly as exicting as Tysons and who's not as beloved, it's tough to say. Beating one top contender after another and being a good self promoter were his biggest factors, but the "0" certainly made everything easier, especially considering that he often hinted at his invincibility in relation to his self promotion. But it's not like it was all he had. Being beloved and exicting would've helped too, but as you see it worked out for him without it.
A Pacquiao rematch would have generated a lot regardless how boring the 1st fight was. An exicting 1st fight would have led to more buys in the rematch, but it wasn't necessarily needed.
The point is: Once something is established among the mass, it's easy to maintain it as long as you deliver good results. It's basic economics, just take the Apple Iphone as an example. Why do people keep buying it even though it's more expensive than all other phones?
R.i.p Steve Jobs. Who did he bequeath all that money to? I would have gladly taken it to take care of it