Commutativeness is handy because it simplifies calculations. HP, in 3.5, is almost entirely commutative, the only exception I can think of offhand is 1st-level HP. Skill points similarly so(but not their investment in skills). Feats are obviously *not* commutative. Outside the above concerns, most base classes are Commutative, with the exceptions of ToB and Ardent.
But that's for 3.5. For this level of nitpicking, I can't answer for 5e.