David, I'm not sure I agree with the doctor who said "almost no one" has AA that acts like yours. We've heard from people with slow-moving MAA before, both here and on Aplastic Central, but perhaps the particulars of your case are different.
At any rate, I think if I were in your shoes I'd seek out an expert opinion right about now. You need someone who has seen more AA cases than most oncologists or hematologists and who is up on the latest research, such as the shortened telomeres angle that Marlene has mentioned. A few names that come to mind are Dr. Young at the NIH, Dr. Maciejewski at Cleveland Clinic and Dr. Brodsky at Johns Hopkins. I don't have any direct experience with any of them, mind you, but just based on the information shared here I would have confidence in any of their assessments of the situation.
-Lisa, husband Ken age 60 dx SAA 7/04, dx hypo MDS 1/06 w/finding of trisomy 8; 2 ATGs, partial remission, still using cyclosporine