The high cost of replacing a top quality phono cart was one of the main reasons I got involved with Soundsmith's Strain Gauge first as an owner, and now a dealer of that product.
It allows the owner to replace the relatively inexpensive stylus in a few seconds, and have an extra stylus or two on hand in case of an accident, or even to just compare the sound of a brand new stylus with the current one in use, and of course to try different stylus profiles for different LP's.
Before investing in this phono cart "system" I used to run my cartridges too long after they had worn, (for financial reasons) which is obviously not a good idea for our precious vinyl collections.
I have always lusted after owning the best phono carts available, but it was not a financial reality, simply because of the wear factor. I don't mind spending five figures on an amp I may keep 10 years or longer, which will still have some value even at that point in time. But replacing a $3500 cart after 2 years (or less since I listen to vinyl almost exclusively) is a hardship which many of us can't endure.
Now that being said, on the digital front, even though there is no wear factor, I believe the cost factor is similar in the sense that a good digital front end can be expensive, and then a short time later due to advancements, the owner may want to try the next latest and greatest, or some new product comes out at 1/10th the price that is equally as good. That very scenario is playing out right now with a just released digital front I am getting this week - it may very well equal a 10 times more expensive top digital rig.