Dear Blizzard,
I'm not sure if you know what a LAN is, but may I introduce you to PAX, Wintereenmas, and the World Cyber Games. Yes, LANs span more than just a household -- they make up the backbone of competitive gaming.
While it may seem trite to link hundreds of computers together with dedicated cable rather than connecting to the ubiquitous Internet, when we're talking about densely-populated events, there are a lot of good reasons to do so. No single internet connection is going to be able to handle the massive amount of traffic being created by hundreds of people playing online games, and certainly not without a perceptable amount of latency. With immeasurable ping times, LANs are superior to any Internet-connected server for large group and competitive gaming. You know, like the original Starcraft that still continues to be played on LANs all over the world.
You may think that giving up on support of LANs in StarCraft 2 will somehow denote the end of the concept, but I think you'll be surprised when you see how well your Internet-only game performs in the professional, competitive gaming leagues. It may be of no consequence to you, but rest assured other LAN-enabled games will continue to take your place. LANs won't be a footnote in history; you'll be a footnote at LANs.