"We don't currently plan to support LAN play with StarCraft II, as we are building Battle.net to be the ideal destination for multiplayer gaming with StarCraft II and future Blizzard Entertainment games. While this was a difficult decision for us, we felt that moving away from LAN play and directing players to our upgraded Battle.net service was the best option to ensure a quality multiplayer experience with StarCraft II and safeguard against piracy.
Several Battle.net features like advanced communication options, achievements, stat-tracking, and more, require players to be connected to the service, so we're encouraging everyone to use Battle.net as much as possible to get the most out of StarCraft II. We're looking forward to sharing more details about Battle.net and online functionality for StarCraft II in the near future."
I'm going to go ahead and emphasize the part of the quote where Colayco says part of the reason is to "safeguard against piracy." If you look at the current state of StarCraft multiplayer, a lot of players use pirated copies to play over services like Hamachi or on emulated B.net servers running custom ladders like iCCup. Blizzard would obviously prefer for the community to be in the same place.
What does a lack of LAN support mean for the average user, though?
Probably not that much. I'm guessing that the solution in place will merely require that gamers validate their copy with Battle.net before they can play any type of multiplayer. After that, B.net will likely be used to setup the games, but gamers on a LAN should enjoy LAN latency after that point.
This is similar to how Relic runs Company of Heroes and Dawn of War II, with the former requiring validation to Relic's own multiplayer service and the latter authenticating with Steam (and then Games for Windows Live if you're playing online).
The biggest impact could hit LAN parties or tournaments. Unless Blizzard has a specific solution for sanctioned events, the organizers will have to maintain an Internet connection to validate all of the players.
What do you think about the lack of LAN support?