I think I may have some insight that will help... I spent some time recently cross-shopping the Sirrus and the Trek FX line, and there are a couple of things I noticed. First, the 7.2FX has a steel fork - this, more than anything, will contribute to the difference in comfort up front. Also, the 7.2 has a more upright geometry than the Vita/Sirrus, which seemed to help a lot with comfort in the saddle.
My impression of the two was that the Specialized Vita/Sirrus was a faster, nicer looking bike, but with a more "nervous" ride. The 32c tires didn't seem to help much with comfort. The Trek was more comfortable, but not as quick. Just to throw a wrinkle in your comparison, both lines actually have three different frames that they call "FX" or "Vita". For example, the Specialized has the base model with the "A1 Aluminum" frame. One level up has the "E5 Aluminum" frame. Beyond that, there is a full carbon version. Trek, of course, has the base FX frame, one with seat stay inserts, and a full carbon version as well.
IMHO, it is totally worth it to go for the E5 frame on the Vita/Sirrus model (which is what I ultimately did). It is a lighter, more compliant frame...and the rim brake model has a carbon fiber fork. It's much more comfy than either of the base frames. If you have to stay in the $500 range, then the FX will be the better option than the Specialized.