It's not always about that. As good as home cable internet connections can be, if you have lots of guys in a living room all trying to play using the same line, lag can start to increase. Not that such LAN 'parties' are very common anymore. Or for those still without cable internet, it's nearly impossible. There are still people w/out cable internet who like to play games w/their family/friends now and then.
For hubby, it's just principle. He doesn't want to suck up bandwidth/be forced to register/login just to sit next to me and play a game pc-to-pc.
As mentioned countless times before, you can still have lan play you must just verify each of the accounts on Battle.net. No lag, yay!