no surprise to me here at all.
I truly believe the UFC is past it's prime, in terms of PPV buys. We have more PPVs than we ever used to, and people aren't going to spend $60 every 3 weeks. In-between that, we have televised events every 2-3 weeks as well.
High quality streams are fairly easy to find, and 1080p torrents are available within hours of the event finishing. Many people will either watch a stream, or download a HQ torrent the next morning, or go out to a bar and spend $20-$30 instead of $60 at home.
The big superbowl, summer and year end events will always sell well as the UFC stacks those cards, but in-between I would expect to see a continual decline in PPV buys. The current model is definitely sustainable for many years to come, but I don't think we see as many PPV buys.