It's not like they wouldn't fit, either-- Northrend has a coast that we'll be visiting, and while it's a little colder up there, Murlocs are pretty adaptable creatures. Plus, the Tuskarr are a race of fishermen-- errr, fisherwalruses-- and they'd probably love to have the Murlocs around, for dinner if for northing else. I'm not sure exactly what an Arctic Murloc would look like, but I'd definitely like to find out.
Then again, as someone mentions in the thread, we'll probably get our fill of Murlocs whenever Blizzard gets around to making the Maelstrom expansion and tells us what all the Murlocs are doing on land in the first place. But until then, while it's OK to leave Murlocs out of Outlands (because how are they going to get there in the first place), it's unacceptable to completely leave Murlocs off the northern continent of Azeroth. Bring on the gurgle!