That's tough. Trademark law is awful stuff, and if Valve obtained the DOTA trademark I could see this complicating matters for the WC3 mod and its community. It seems perfectly reasonable that Blizzard wants to cover their butts here, although hopefully it can be sorted out in such a way that Blizzard is protected and Valve can obtain the trademark.
I'll go with Blizz on this one unless Valve hired the original DOTA map creators to develop their DOTA.
IceFrog is working with Valve on the project. Steve Feak isn't, but if he's opposed to Valve's DOTA 2 I'm not aware of it.
Valve like to get their hands on MODs and turn them into full on games.
That's where "Left 4 Dead" came from.
The guys who made the MOD apparently didn't get paid.
Of course I've only read this on the interweb so who knows how much truth there is to it.
The situation with Valve and Turtle Rock was weird, but I find it hard to believe the TRS devs never got paid.