Update from Michael Rome:
On Wrestling Observer Radio tonight, Dave Meltzer said that the 1,010,000 buy number is confirmed for UFC 91.
The number is actually amazing all things considered. The UFC just let the show sell itself, they did a lot of media but they hardly promoted it as well as they could. There was no "feud" between the fighters, no cross promotion with WWE or TNA, no TUF buildup, and no multi-part series. I recall the level of hype the UFC put together for Hughes-Gracie and Chuck-Tito, and this fight just didn't have the same kind of thing.
So what did it? Maybe it was the ad calling it the biggest fight of all time. Maybe Brock Lesnar, who was able to draw 600k against non-draws, all of a sudden became a mega draw against an established star. Maybe the return of Randy Couture excited all the UFC fans to see Lesnar get beat. Regardless of the reason, they lost to a huge ODLH fight by only 240,000 buys in a year where they did a lot of great buyrates.
All things considered, millions of people saw the UFC 91 card, and it was a card very easy on casual eyes. Tons of quick finishes, a decisive main event crowning a new star, and a rabid crowd.