The PPV numbers point more to the marketing power of the Spike shows then anything to do with the fighters themselves.
Most of the top draws are, not suprisingly, guys that the UFC has invested heavily in putting on free tv (e.g. coaches on the TUF).
So while I have absolutely no interest in seeing Ken Shamrock fight at this stage of his career (still a legend), if the UFC puts him and Ortiz on tv every week acting out a WWE style gudge match, lots of casual fans buy the PPV.
I am not saying that their fighting ability has nothing to do with it but my point is that it is not the main driver of the draw.
Dana wants Rampage to be a star because he has star power. So he delays the LHW title for almost a year so that he can get him as a coach on the TUF.