I was always told that scopes were designed (internal springs, etc) to have the elevation and windage turrets positioned at the 12 and 3 o'clock positions.  This is further supported by the various range finding types of reticles that require the scope to be mounted in a 12 & 3 o'clock orientation in order to work.

But occasionally, especially with the rapidly growing popularity of red dot sights on "combat" guns, I see the turrets being positioned at the 9 & 12 o'clock positions.  Is there any particular reason why folks are doing this?  

BTW, it'd be kind of hard to do with an EOThingy, wouldn't it.

the aimpoint is set up like that mainly because its a combat optic and having the option to use free hand to work the knob is the shizznit.