Obviously younger guys tend to grip it and rip it so a drop in velocity is expected for lots of power pitchers, but Felix is taking it to a new level. It's clear he's learned to pitch more than throw, but the mph he's lost the last 3 years is what scares me. This will likely be his 5th consecutive year with 230+ IP, you don't see this sort of usage without eventual deterioration. Luckily he has other great pitches and doesn't rely solely on his fastball.
He did picked up the use of his sinker in 2010 and he throws the majority of the time now v his 4 seamer. His sinker has declined in velocity step by step with is 4 seamer also.
His K/9 has increased every year since 2007. One thing is he's giving up some velocity for the sake of movement. He's seemed to increase his movement on his slider and curveball compared to when he was throwing mid 90's.
Either way it should be interesting to see how it works out. He can't continue the trend of dropping a mph off his fastball every year. Luckily for Felix the mariners blow so he never has to pitch in the postseason.
I think this was the year that a few people started to project he was going to start to slow down just a little bit, in terms of success. He is still young. Also, he could just be a fricking horse like CC is. Not every pitcher is the same. It would not shock me for him to be a Cy contender for four more years despite his velocity decline.