Losing hasn't been exclusive to "Pride fighters" in the UFC.
It's an epidemic in MMA overall and speaks to the volatile nature of the sport.
Who hasn't lost recently?
How many top-ranked fighters who have been active, and who have also faced more than one ranked opponent, have NOT suffered a recent defeat?
Off the top of my head - Fedor, Chuck, Anderson, Filho (Shogun and Lindland if you don't want to count losses to higher weight-class opponents)...
So about 5 guys in the whole sport?
Sounds like losing hasn't been confined to any one org. in particular. It's pandemic in MMA. That's what happens when there are so many unpredictable ways to lose.
Upsets have occurred betw Pride and UFC fighters, within Pride betw Pride fighters, and within the UFC betw UFC fighters. It'll happen again. Has more to do with MMA in general than any org. in particular.