I'm glad to hear about your recovery, and sorry to hear that the cause of your OH was not properly investigated. There are a number of causes of OH, from medications, to nerve damage/loss, to venous insufficiency, and there is specialized testing that can help to elucidate the source of OH/dysautonomia but it is only offered at a handful of top hospitals in the US (and indeed worldwide):
http://www.medhelp.org/health_pages/Neurological-Disorders/Dysautonomia-Specialists/show/717?cid=63
I think it's unlikely that *most* cases of OH are curable through tilt training, given the number of cases of OH that are caused by neuropathy, baroreflex failure, etc. but certainly there are some who can benefit and it's wonderful to hear that you have had such success! The hospitals I mentioned above may incorporate things such as cardiac rehabilitation into a treatment plan in order to help improve the return of blood to the upper body in the upright position, and this is helpful for many patients; one of the largest barriers is getting insurance to pay for the therapy. As your case points out, we still have a long way to go in this field.