I gotta be honest, I not currently nor was I all about OMT when I started, and I certainly don't believe it can cure everything on everyone (I'm pretty sure we are past that type of panacea mentality). That said, I think the main issue with OMT is that there is no really effective way of knowing when it will "work" on someone to relieve their pain. I don't think our methods of knowing when to apply it are fine tuned. That said, at this point in time after witnessing some people actually benefit from it, I am not going to reject it blindly (nor am I going to accept it blindly).
Also with regards to the comment that if it were really effective then people would be treating themselves all the time, how do you know they haven't been? Before I even knew what a DO was, let alone CS, I would try to get myself into a position of comfort (as most people would). Sometimes it would work, sometimes it wouldn't. Unfortunately, sometimes it requires some help from another person to do that. It also requires being motivated enough to do it, when say you are too tired to fix your mild discomfort and would rather just sleep, because you need to wake up early for work/school/life.
People could also keep themselves healthy by eating right, or exercising, or keep their immune system up by just sleeping more regularly, yet simply because they can do those things, doesn't mean that they do do them, especially when they have other problems or responsibilities to deal with.