Why are some similar controls (Rads) either Axes or Buttons?

[E_Davjack]

For instance, on the 109, if I disable the automatic Prop Pitch or Water Radiators, those have to be bound to keys, one key for increase and one for decrease.  However, on other planes, the Prop Pitch (RPM) or Radiators are bind-able to an Axis, such as on my Saitek Throttle Quadrant.  The axis approach is infinitely more user friendly.   

 

What's up with this?  Why cant all water radiators on all planes be on the same axis?

 

Does it have to do with modeling the controls for each aircraft?  Because even if a 109 pilot is cranking a little wheel instead of pulling a lever, wouldn't it be much more intuitive for the player to be able to use an axis, sort of how a real pilot would know how many turns = 50%?