A good cook doesn't need to own 5 stones to sharpen his knife, he just needs to have the number of the sharpening guy.
It is also a very wholesome and meditative activity.
Most piano players don't have a clue about how to tune their pianos, though.
Most professional musicians know their instrument very well - and still know a man for the "hard" stuff, e.g. for thorough maintenance or repairs that require craftsmanship.
And there are obviously variants. The guys that fix their instruments regularly and experiment with e.g. cooking your stings, and musicians that hand them in for the tiniest, easiest tasks.