Yes, you are missing something: if DU developers get pissed off by some XDA thread or user, they could stop tuning and releasing the ROM for our device.C'mon ungeeked...
The DU server hosts, as far as I know, free and open source files that can be legally downloaded. It's a public, official server. No one is creating mirrors, claiming to own or to be the developer of the ROM, so I can't see which XDA Rule would we be breaking.
On top of that, you just can't stop people from posting links to your website. I have websites and don't like Facebook, but users still share "my" links there. Should Facebook stop that from happening? Can I stop them? Of course not!
They don't have to create threads here nor like XDA. Now, not allowing people linking to their website or speak their minds on a website they don't own? Either I'm missing something or many around here don't know how the internet works.
It's as simple as that, so if you are like us and want to use and discuss this ROM just respect what the developers want, that is what Ungeeked wrote above.