I must be either very careful with my brushes, or just not paint a lot, but I've got just a small batch of brushes, most of which are years old.
My number one selection consists of 4 of the 5 brushes from GW's Deluxe Paint Set (or whatever it was called; it's a fancy wooden storage box for brushes) which I won in a painting contest during a tournament in 2006. They're W&N Series 7. I've even got one W&N Series 5 size 0 brush I bought in 1996, when I started out at the Academy of Fine Arts, and still use as my number one in its size to this day!
And I don't even pamper them with brush soap etc all that much (although I do have it, I just never get around to cleaning them

).
My oldest one is a GW one I got in one of the first paint sets I ever bought, possibly back in 1989. Now, that one is plenty battered and bruised, but it has been my 'transfer brush' for many, many years (meaning I use that one to transfer paint from pots to my palette), but I have been known to occasionally still use to apply paint on minis. It's seen less use in the past 5 years though, as I've switched almost exclusively to Vallejo dropper bottles now.
New brushes per year for me, can be counted on the fingers of one hand, if at all; in years of very low productivity, I've just not bought brushes at all. And when I do buy brushes, it's usually W&N size 0000 ones, as those tend to wear out the quickest (use them a lot for very fine details and freehand script).
So yeah; brushes for me are not disposables, but rather they're an investment. You get to know the properties of certain brushes, using their 'defects' as advantages. For one person, a curved tip on a brush is reason to discard it, but to me, this is now a specialized tool for certain jobs, because I know the way it behaves intimately.
I once read or heard that (I believe it was) Jen Haley would discard her sable brushes after painting only a couple of miniatures with them, as they would be losing their factory perfect tip. To me, that's just wasteful. My father always taught me to take care of my tools ('and they will take care of you'

), and I've always applied this not only to the tools in the garage, but also to the ones on my hobby desk...