as one who could not possibly care less about DOTA, can someone summarize this mess for me?
Dota is a mod of Warcraft 3. Has had dozens of people work on it over the past 7 years, has had several major project heads over seeing the mod throughout the years (The three biggest are Eul, ported a custom map from Starcraft and made a Warcraft III mod of it, Guinsoo, who now works at Riot games who make League of Legends, and Ice Frog, who still manages the game to date and has worked on it for about 4+ years)
Valve decided to do what Valve does, and pick up the mod's development team and remake/make a sequel of it (See Team Fortress 2, Counter Strike, Day of Defeat).
So, one legal battle that Valve may have to fight is if Dota can even be copyrighted or if it is public domain. Personally, Blizzard may be better off trying to prove the Dota name is public Domain rather, since then they can call Blizzard Dota Blizzard Dota.
Also, some staff at Riot Games, makers of League of Legends, and who formally worked on Dota in the past, have put up some fight over the trademark.