Again citation. I know of zero valve games that do this. They certainly do not advertise if they do so, im a huge fan of many of their games and would know about this, not so much for WoW, but for a couple valve games ive been following for years: TF2, CS.. I would know, I'm 100% positive they NOTHING like mournlands.I can name non-MMO's too- Valve for all their games.
I know for a fact both WoW and most the big valve games (CS, TF2) have PUBLIC OPEN test version and servers unlike DDO. They also have bug report forums and read every report. Thats the major difference. Open, transparent QA that is very clearly reading and responding to a lot on dedicated bug report forums, they have great QA. How frequently TF2 gets updates and few bugs it has is awesome.
If they also have a hidden un-advertised closed one, that is a good thing. And thats absolutely not the same thing.
"We have this great preview server, we keep talking about it.. and no you can't join, and no we have no test server." is a lot different then saying nothing, advertising a open public test server and having a hidden one out of sight for earlier stuff.