I'd rant about this, but let's be honest. The surprise isn't in GW breaking this promise, it's that it took them so long to break it.
GW needs sales, and this (very good) game is the lowest of low hanging fruit. The design, plastic molds and card-cutting dies are already paid for. So all they had to do was print up a page or two of new rules and some 'exclusive' room tiles to be able to call it something "new" (and bait the compulsive collectors).
Cash grabs don't get much easier than that.
Kudos to @Luke_Retallack for the pic!