The practice part of the game engine also takes height into account. The 5'8 player can't improve as much as the 7'4 guy.
Small, but important, point: the shorter player won't improve as fast but can improve as much.
Someone correct me if I'm wrong here.
If they are trained the same number of seasons in inside skills, the 7'4 guy should increase his inside skills more. The smaller player could improve as much or more, if he trains longer.
So it is a practical limit, rather than an absolute limit.