Is there a reason that 0 Degrees is along the Y axis instead of the X?

I ran across something that is puzzling me. I was getting some strange results when tweaking the angles of moving objects because I made the assumption that 0 was along the X axis going to the Right, 90 is along the Y axis going up, etc... But alas this does not seem to be the case. I wrote a simple function to echo the Angle, Speed, and (X,Y) of the object when I hit Space. Upon hitting Space at a few key spots with the object moving at certain angles I discovered that the whole angle system was turned on it's side. 0 is Up, 90 is Left, 180 is Down, and 270 is Right. What puzzles me is WHY this was done. I do not see a logical reason to turn the Angles on their side like that. I am hoping someone at GG can satisfy my curiosity.