Well, when I was in highschool, I was 5'9 3/4" tall, which I always just rounded up to 5'10".  Prior to HRT, I measured at 5'9 1/2".  Well, now I'm 5'9".  I had heard about losing height due to HRT and I thought that was cool.  You also lose height due to age as well.  I know my dad has lost an inch from what he used to be.  So I think it's really a combination of the 2, but the transsexual seems to lose the height much more quickly.
Melissa