I will always respect Blizzard. It's not because their games are polished, have a fine-tuned balance, and look presentable (although they are), but for the simple reason that Warcraft III introduced me to modding. My experience in RTSes is far from complete, but WCIII is the only RTS I have ever played that allows such sweeping changes in gameplay through its map editor. This is not to say that the editor isn't buggy and, in some ways, annoying incomplete. Those things don't matter too much. The editor is there, and it works well enough to foster a community of mods that turns Warcraft III into a library of games, many of them far better than vanilla Warcraft. DotA is, of course, the most well known and one of the most polished, but it's really on the shallow end of what can be done with the editor.
With Starcraft II, Blizzard has promised to make the editor even more powerful, and thus earned themselves my money. The premium maps feature is not something I expect to work in terms of growing the modding scene, but it's a noble effort. Currently, Blizzard gets 100% of the profits that result from custom maps (It doesn't seem too unlikely to me that people would buy the game in order to play DotA). Their offer to share some of these profits is quite prudent on their part, and if it results in even one map worth the price, it will have succeeded.