To give Valve an extra week to fool around, right? Seems that DotA 2 staff are too lazy to do their jobs correctly and in a punctual manner.
They might just remove the test server. I think this sh1t is pointless.
Btw, there is no new hero this week, as they announced Bane last week.
http://blog.dota2.com/2012/03/now-your-nightmare-lasts-forever/