.newsbeuter/urls holds all the links to subscribed feeds, should you have configured newsbeuter to store those locally, rather than using online services like The Old Reader, which is more secure since it means you don't have your login information in Plaintext, especially if you're synching your configurations.  
It's an optional, but I figure anyone that *does* save their feeds locally, would want to synch those with their configuration to another machine as well, instead of having to set those up every time. 

With that in mind, and the fact that mackup seems to only copy files that already exist anyway (from a glance at the code at least) I opted to add it.