Valve announced DotA 2
There could be two possible reasons why Valve registered extra TMs:
1. Valve is working on a DotA Trilogy.
2. They are very serious about their future so no competitor can take their place.
Reason 1 seems more appropriate because, just one day ago when these Trademarks were filled, Valve Corporation co-founder Gabe Newell said in a magazine interview that "We have three pretty big surprises in the next 12 months at least." Lets see what Valve comes up with.
You can find the status of DOTA 2 & DOTA 3 trademark at United States Patent and Trademark Office website:
http://tarr.uspto.gov/servlet/tarr?regser=serial&entry=85121910 (DOTA 3)