I discovered that for some reason CSS won't read image names that contains '@2x' (indicates that image is for retina), so for example, this will work:
#play { background: url(../images/layout/play_2.png) no-repeat; }
and this won't work:
#play { background: url(../images/layout/play@2x.png) no-repeat; }
It is the same i all browsers and across devices (iPhone, iPod, iPad). Any idea?