According to early estimates from Dave Meltzer, UFC 128 generated between 415,000 and 470,000 pay-per-view buys. This is a fairly impressive number considering the fact that in February, UFC 126 did between 700,000 and 750,000 buys. This is in addition to the UFC sneaking in UFC 127 and doing between 250,000 and 300,000 buys with a fairly weak card supporting a non-title main event.
The real genius of the UFC's business model is that between events like UFC 127 and UFC 128, Zuffa pacifies paying customers with free cards like UFC on Versus 3, which came earlier this month, or events like the Ultimate Fight Night card this weekend. After this weekend's show, Zuffa presents Strikeforce: Diaz vs. Daley on Showtime in early April, and then will likely do monster numbers again with their most consistent pay-per-view draw, Georges St. Pierre, headlining a stacked UFC 129 card at the very end of April.
Quite frankly, talk of slowed momentum is completely unsubstantiated. The UFC typically does big numbers, modest numbers, strong numbers, and then big numbers again. There really isn't anything that can consistently produce the kind of numbers that UFC events do. Boxing can certainly do big business a couple times a year, but the UFC simply does more shows, some of which do comparable numbers to the biggest drawing shows in boxing. The WWE at one time was the king of pay-per-view and really blazed the trail for the UFC, but their numbers are on a steady decline.
The fact that Jon Jones' assault of Mauricio "Shogun" Rua was "only" able to pull down 415,000-470,000 buys is no slight to Jones, and is in no real way a reflection on his drawing power. At this point, the UFC is simply doing such big business that it's hard to imagine how Jones and Rua could have gotten much more than they did. It just so happens that Jon Jones dominating Mauricio Rua was sandwiched in between pay-per-views featuring MMA's top two pound-for-pound fighters. Some might try to spin this into an indictment of Jon Jones' drawing power, but the UFC and Jones are likely laughing all the way to the bank.