Since other people are also chiming in, in my game it works like this: crippled characters and NPC are a rarity because restoration magic can heal all but the worst aliments. The only exceptions are those who are worshippers of Illmater (as the god of sacrifice and martyrdom, it is thematically appropriate they refuse to heal crippling wounds), or those who do it for an important reason.

For an instance of the later, I am running a campaign set in a "sky pirate" sort of style, and the main Pirate city has an Orc as its mayor who has a prosthetic right arm. Or so it seems, because he actually has a symbiotic relationship with a Mimic (the Mimic helps protect him, he makes sure it is fed gold on the regular), and the "prosthetic" is the Mimic.