Salt Lake is not entirely flat. It's on the western slope of the Wasatch Mountains. The cost to lay fiber is more closely tied to availability of existing infrastructure (dark fiber), regulatory burdens (or lack thereof), subsidies, typical density (single family vs multi-tenant), etc.
I get the feeling that regulatory burdens is the biggest problem. I know that the laws in California are preventing them from offering the service there, and in Oregon they are waiting on a bill to pass before they will come to Portland.
