"It works" just because. No satisfactory reason is given at all, except that creatures possessing spell-like abilities, "just have them".
I always get a laugh when you criticize other people's logic.
Anyway, it makes perfect sense to forego material components rules for all but the most expensive. Again, having the wizard (and sorcerer, meh) player waste time managing components and carry around a load of different components is only good to clutter the game for that player, and possibly the others as well (as I explained before and you failed to understand). It makes sense to use material components for powerful spells (Wish, Miracle, etc), so as to prevent casters from spamming those spells to victory everytime. Stoneskin can hardly break the game. Wish, on the other hand, is a very different matter.