Community generated mods are great and both Valve and Blizzard have a history of supporting communities because they believe in 'long-tail' sales on their infrequent releases.
But, when it comes to creating commercially developed top-tier games, Valve is the company that has spent the time and money to take fan created games and turn them into top tier gaming experiences. Warcraft III is great and all, I bought it back in the day, but I don't still have it installed on my PC, nor do I want to monkey around with mods for that game. I look forward to a commercial DOTA game from Valve, and whether they get their trademark or not, I trust that Valve is not doing this for anti-community reasons. They never have to date, and I give them the benefit of the doubt. Blizzard on the other hand... take a look at the things that generate headlines with 'Blizzard' and 'community' in them and you'll see that not everything is that rosy. This comes from a long time Blizzard fan who doesn't like the direction things are going now that they are part of Bobby Kotick's community-hating empire.