In the corporate world, laptops and desktops are typically retired after three years. I have experienced this at large and mid-size companies. Corporations often lease the equipment, as it makes the bean-counting (and financial manipulation?) easier. That is one reason you can find hard-used, 3-year-old Dell and HP machines in quantity on eBay. (And, no, I would not recommend investing in these machines.)
The analogy to car depreciation may not be numerically accurate, but leasing is mainstream for business computing equipment.