Well, I guess I might as well come out to at least this little section of the forum ^^
I am a transexual. Have been one since birth, in my eyes. I'll have to agree with Sammi. If you are a transexual you know it. However, as stated previously, there are different forms of transgenderism, which vary from sexual excitement from dressing in the "opposite" sexes clothes, to varying levels of...empathy, for lack of a better word.
There aren't any "knowns" when it comes to this issue, since transgenderism has been pushed aside for serious studies. Society has improved on it's acceptance, in my eyes, but there is a long way to go.
It's up to you about coming out. It's hard, and it can have detrimental side effects. I don't want to go into any personal details as of yet, but suffice it to say that my life had what I would refer to as a huge hiccup when I revealed my little secret. As things currently stand...the friends I now hang out with don't know, and my family thinks I'm "cured" (forsoothe...I laugh).
Everyone has there own experiences, and please understand that my circumstances are, and have always been, on the rigid side of things. Hopefully, most people won't have to experience anything so harsh, and most don't. ^^
As for the reason that many transgenders identify with ab/dls...a few theories. One, is that many transgenders feel (rightly so) that they had their childhood ripped from them. This could be considered somewhat of way to make up for it.
Also, many transexuals don't feel comfortable with their genitalia, and if you're diapered, it creates a bit of a buffer, so to speak.