Unless we are talking buzzcut, there is no point in doing this, and not every avatar has a "standard" skull.
Low shoes don't need to be rigged, they also don't need to be a single monolythic object, we don't have a toe bone.
A lot of calf and ankle heels don't need to be rigged, in fact, the "broken ankle" look is a lot worse than a stiff looking ankle on most of those.
Unless it's for some animesh furry avatars, ears will never move on their own.
But also a lot of neckaces, glasses, bracelets. IF IT DOESN'T DEFORM, IT DOESN'T NEED TO BE RIGGED.
Typically if it's rigged:
I can't rez it as a decorative prop.
I can't wear it somewhere else.
I can't tweak the way it attaches.
I can't make it bigger or smaller.
I can't use it on my <insert avatar brand> avatar.
Each of those bulletpoints is a lost sale.