Ah, I see...TMG allows me to have all my domains pointed to 1 IP (since that is all I have from my ISP) and be able to inspect what address they are going to and route it to the appropriate server inside my network. IE:
Public domain <- pub IP -> Firwall <- local server ip
www.blah-fake.com <- 126.96.36.199 -> TMG <- server1.local
www.derp-fake.com <- 188.8.131.52 -> TMG <- server2.local
Dydns gives you the IP address translation from the world to your external IP. Your router gives you the IP address translation from your external IP to your internal box. I can feed separate requests to 65,535 individual servers without using a product like TMG. (Logically - physically that will have to wait until we have much faster routers - and internet speeds.) TMG seems to be just a huge (too huge) filter for the totally paranoid, built on the usual "we know what's best for you, so don't look too closely" MS philosophy.I use dyndns as well and it would handle multiple domains just fine if they were hosted on the same box, but when you have separate web servers is where tmg comes in to play.