The reasons are several:
- in Safari, most of the screen is used for text display -- and mostly only text -- rather than fixed sections in the news apps for ads and other distracting graphic elements that reduce text area. (To view news photos, I use AOL's Pixcetera app)
- it is more convenient, efficient and less disruptive to email articles on Safari by using the toread.cc bookmarklet. No need to jump into the Mail app, and back again to the news app currently in use
- there are fewer iPhone apps to carry around
So, if you prefer text for your news, go Safari. But stick to iPhone apps for graphics and charts.