I think this isn't true anymore, except in a very gross sense. Like, every restaurant in Deer Valley and Park City sells wine and/or beer. I'm pretty sure we got drinks at restaurants in Salt Lake City, too. It could, conceivably, be that only non-residents can be served alcohol, but I think I heard that wasn't the case. You're just not supposed to drink if you're Mormon, and the laws are not strict about production, sales, and consumption. Maybe you can't drink at home?
I don't know. I just ski there, but alcohol is easily, legally, available everywhere I've been in Utah.