Either the AMA or FDA hasn't approved Buprenorphine for the treatment of CP, but some physicians will Rx it, I think they're not comfortable doing so because it takes extra certification to Rx it for opioid dependency, so they don't bother to read up on it, they can Rx it for pain, but most won't.
Here's some physician resources on Buprenorphine which might answer some of your questions.
http://www1.buprenorphinecme.com/PageReq?
It seems to me the cost factor vs. traditional opioid therapy for the long term CP patient doesn't make it cost effective, and it appears Bup has difficulties in the perioperative management of pain as opposed to opiates.
HTH
Cats