Here is a screen shot of the pitch selection for last night's start by Mike Pelfrey.
Now, I know that pitch f/x is still a baby, but I also don't see a splitter on that list. And I don't remember everything from last night's game (I blame beer and the basketball game), but I do remember very clearly that a splitter was mentioned. So which pitch is it? Here's a screen shot of the locations of the pitches.
From this screenshot, I would guess it was the change that is called the splitter, since they all show up in the bottom of the strikezone. The good news is that the changeup got whiffs 13.3% of the time yesterday and 16.7% of the time this year - provided it's the same pitch we are talking about here. The bad news is that Texas Leaguers also says that the change doesn't drop half as much as his curve - 4.50 vertical inches of movement for the change, and -2.27 for the curve. Compared to his 8.81 number on the fastball, the changeup is dropping, but I guess we can forgive the pitch f/x system for not calling the pitch a splitter.
It's also worth noting that the BIS section of FanGraphs shows that Pelfrey is throwing a (new) splitter 4.8% of the time this year (at 84.7 MPH, close to the 83.2 MPH speed of the changeup), and that the splitter has already been worth 2.1 runs in linear weights. Since the speeds are close, this is another notch in favor of the changeup / splitter link.
One last screenshot - spin movement w/gravity by type for the year. You'll see that there seem to be two groups of changeups, with one dropping further than the other (or am I imagining things?). It seems like the splitter is indeed mixed in with the changeup, and that BIS is out in front of MLB pitch f/x on this one. (PS: just checked Edward Mujica's page, as he's famously added a splitter this year, and it has the same problem. Guess MLB pitch f/x doesn't like the splitter.)