(A) The differences approach the trivial on some instruments, but not all, and
(II) (People who really know elementary physics please don't murder me
here!) Even if the percentage point of the fulcrum is very close, isn't the
different (not trivial) length of the sharp lever going to make the
distances travelled by the arcs of the two ends of the lever quite
different?
 
What feels wrong or screwy - and I agree with Bill that it's much more
noticeable on, say an Italian, than on an instrument with key levers 25
feet long - is the key travel and the stagger.
 
It also, once again, needs to be remembered, that it doesn't take
sloppily-installed key pads for there to be tiny differences from one to
the next. And the degree to which the padding mats down over time may be
different (IS different in actual practice).
 
So what happens is that the jack is suddenly sitting on a pad that's been
matted differently, or, not infrequently, sitting on a "virgin" part of the
neighbor's pad.
 
It is the inappropriateness of the jacks' heights which you notice most of all.
 
owen
 
Still: It's not a problem if the player simply accepts the odd feel without
complaint.