It's not part of a minimum viable product. When you're trying to get something out the door, your downtime communication is not your top priority, so you can afford to improve it later.
Agreed. And they did use their Twitter accounts to communicate the problem/downtime (which even MVP's should have & use for status communications). You can be sure their status.foursquare.com blog won't have any more information than their Twitter accounts when they have unexpected downtime in the future.