The poster above is by Ron Garney, and his mission seems to have been to take a classic Jack "King" Kirby cover image and "modernize" it. That's all I can think of.
This cover image has been an iconic one for decades, used many times over as the gallery below demonstrates.
I'm not quite sure what Marvel is trying to accomplish with the new poster. Perhaps they think the classic Kirby image lacks some punch somehow. Seems like the original would work fine for a poster. One detail that struck me is that while the Cap figure is larger in the Garney version, the shield is the same size in both. Hmmm.