The correct answer is - YES

Those who focus on the vertical classics or vertical shmups usually mount them vertically.
Those who are more into the 90's fighters usually mount them horizontally.
Not sure why, but horizontal games on a vertical monitor look tiny and awkward to me.
Vertical games on a horizontal monitor don't bother me as much even though technically they are the same size.
Could be that I'm used to horizontal games with 25" monitors, but only 19" monitors on vertical games.
Some don't want to decide, so they rotate:
http://forum.arcadecontrols.com/index.php/topic,108897.0.html