Is the DETC limitation of the no docs except for first professional degree self imposed or imposed by some other situation/organization?
I think it is an agreement with the Department of Education's Office of Accreditation and State Liaison. Don't know if it is formal or informal, but the sense of it seems to be: "Do this for a few years, and then perhaps expand to include all doctoral programs." I still don't understand how DETC can accredit non-US schools with regular Ph.D. programs, such as the University of South Africa, University of Leicester, and Open University of the US.
DETC has simply chosen not to expand their scope to include doctoral programs. I believe this has to do with a simple allocation of staff resources rather than any agreement with any outside body. There are more important to issues to address at this time. There doesn’t seem to be a strong demand from DETC schools for such an expansion. At the most recent DETC meeting in Tucson, I heard no discussion of the subject, formally or informally. I expect DETC will authorize a pilot program for doctorates in the next year or so (just my opinion, not based on any inside information).