While this isn't an issue I've personally followed, it would seem that this was one of those things that everybody knew but nobody wanted to admit. When StarCraft II was revealed not to support LAN play, some were understandably upset and became angry that it was probably down to the fact that they were being punished for somebody else pirating the game. Well, nearly two years after initial release, director Chris Sigaty has admitted that, yes, you were unable to play LAN games thanks to Blizzards concerns about piracy.
According to DSOGaming, Blizzard were becoming increasingly annoyed that Warcraft 3 and DOTA were still as hugely popular as ever but that most people were downloading the base game illegally in order to play them. They also felt that it would be better to have a connected experience, rather than an isolated one, although this seems like an attempt to soften the "piracy" blow; why couldn't there be both?
Sigaty went on to say that LAN wouldn't be coming back to the series any time soon. No doubt there are pirates out there enjoying it right now, but the less stating the obvious in this case, the better.