The original creates the perception of realness and dimension through the effect of wiggle stereoscopy.[1]
Wiggle stereoscopy: http://i.imgur.com/FhA9aZI.gif
In contrast, the Pix version removes that sense of depth, and turns it into what is essentially a cinemagraph.[2]
Cinemagraph: http://farm6.static.flickr.com/5303/5659130034_7fc3dcfb8c_o....
[1]https://en.wikipedia.org/wiki/Wiggle_stereoscopy [2]https://en.wikipedia.org/wiki/Cinemagraph