In that thread you linked to, the person said that the Hughes techs were idiots. Basically, before you purchased the static IP, your modem had a randomly assigned IP address, your computer had a private address, and the modem translated your private IP address to its random public one. Once you purchased the static IP, you got one that you could configure on your PC, but the techs didn't tell you that, so you still had the private IP assigned, and the modem continued to translate your private IP to some random one.

However, none of that should really have a huge bearing on your VPN access, since you have "NAT Traversal" turned on in the VPN client. I could go into why that makes a difference, but neither you nor anyone else cares.

What I'm getting at is that I doubt that there's a difference between you having purchased a static IP and not using it, like you were doing until you changed your PC's network configuration, and not having a static IP at all. So, if I were you, now that you have the VPN working, is reconfigure your PC to use the private address, and then test your VPN client again. If it still works, drop the static IP service. If not, keep it. There is the possibility that there is a difference between the two states, so it's vaguely possible that you'll drop the static IP and the VPN will stop working, but I doubt it. If so, though, you can always have them give you that service again.