The few DOs I know do not really practice osteopathic medicine and when I asked one of them whether or not they used manipulative techniques I was told that they did but only "when no one was looking." This implies that perhaps there is a negative opinion regarding DOs in this area.
Actually, the reason is not as sinister as what you may suggest or conclude. During rotations, esp in the primary care settings, I've met many DOs choose not to actively do OMM because they don't want their practice to become an OMM clinic.
The public is accepting of OMM more than DOs. Take a look around at the plethora of chiropractic clinics and natural herbs/supplement business. Also realize that low back pain, degenerative joint disease, and shoulder problems are VERY common conditions seen in the primary care setting. Add to that the millions who work demanding physical labor, and you have the perfect set up to do OMM everyday all day.
The problem is ... most DOs don't want to do OMM all day everyday. Hence why the "if no one is looking part." If a patient has a shoulder problem that is helped with OMM ... that patient will probably return for future problems. That patient may also refer their friends (who also suffer problems) to you. If their friends get relief, they will refer their friends. Soon, the majority of your patients will no longer be your typical primary care stuf but all "my back hurts" and "my shoulder hurts" and "my neck hurts" and "my knee hurts"
Insurance/HMO reimbursement is not an issue. In the Philly area, Blue Cross and Aetna do reimburse for OMM ... BUT if you can offer relief to patients, many are willing to pay CASH. (just think how much money is spent each year on OTC pain reliever, natural supplement pain reliever, chiropractic care, etc). And if you talk to ANY doctor who is trying to improve their income, it's all focused on cash-based procedures (ie., botox injection).
On another note: DOs do make 5% of all physicians in the US - but also, the distribution of it is not even. You're not going to find 5% DOs in Alaska, Alabama, or Washington State. You will probably find > 5% DOs in PA, Michigan, Florida. New York is a big state - and you'll probably find the same uneven distribution.