If they're anything like the place I work at it comes down to mindshare. Yes, it's just consuming a Twitter feed and maybe some other proprietary datasource but some exec "needed" an app because then our logo (icon) is on the phone's screen. It's visible and quick for people to access the news feeds instead of going elsewhere.

Sadly, most of the decisions we question are driven by marketing.

Having been pretty close to many mobile apps that came out of NBC in the early boom days, I can confirm that this was the case for many/most of the apps I ever touched. Most of them were pretty bad, just RSS driven web pages in a native wrapper. Getting the brand onto users' devices was the primary goal, experience be damned. I can't speak to Breaking News, that was a different team.

The Twitter feed is a sub-set of their content and postings.

You should have checked out the app, it's pretty great. You get push alerts on the topics you want and [optionally] where you are located. You can also use it to report breaking news and as a result they had a nice jump on a lot of stories like Earthquakes and the like.