While reading PDF documents in DTP and using the keyboard to click to the previous or next page, the up/down arrow and page up/page down keys are used. Ever notice how their directions are completely reversed from Apple’s Preview, where we open in external viewer most often? I think Preview is the most intuitive. I hope DTP may conform to the Preview key functions to make this PDF ruled world a bit smoother.
In this case the arrow keys are handled by Mac OS X and Yosemite introduced a reversed direction if continuous scrolling is disabled. But you’re right, it’s probably about time to fix this.