Because there is no 'server' int the way other RTS's have it. Everyone is technicly spoken a client and server while playing.
Most (if not all) RTSes are peer-to-peer. I don't think I've ever seen one where you didn't have to port forward to host.
I agree that demigod brings some evolution, but when you want to dominate the market, make a sucessfull tournament rts game, a company should point to the best solution, best service that can be provided. As demigod works right now works, not very well, but works, but i will wait and see how easly it can be hacked by malicious users.
Dedicadted servers would be the best solution, and you can't argue agains that. It costs more, is true, but so does everything you want to be top notch.