MTV Geek talked with Tim Brevoort from Marvel about the new character designs that are a part of the upcoming "Marvel NOW!". Here is an excerpt talking about the changes to Captain America, which you can see below:

The approach and the thought was very simple: we wanted to modernize Cap’s outfit so as to reflect the gear worn by actual soldiers, to convey that sense of the character visually. 

We weren’t really thinking about the movie incarnation per se, though it’s difficult to avoid it I suppose. But even there, Cap’s already had two completely different suits in the movies, in CAP: FIRST AVENGER and then in MARVEL’S THE AVENGERS. What we were really going for, more than anything, was the feeling of Cap being an actual soldier. At the outset, I did some research and collected a bunch of different photographs of modern military gear, helmets and what-have-you, and they all informed the design we eventually settled on.