In my opinion though, that kind of takes away some of the fun. Knowing that there's only so many DNs and that if they're destroyed you won't see more until a new one is built, it makes it a lot more exciting when you see a big ship online.
Also trying to hunt and trap the other sides big ships is a lot of fun, knowing that even if I kill this dread there's just going to be another takes a lot of fun out of it for me.
But then that's just my opinion, and the server admins can do whatever they want.