The standard corporate replacement schedule at the companies I've worked at has been 12 months for Windows laptops and 36months for Apple laptops
A fair bit of that is because Windows runs like a bag of s**t without an absolute ton of memory and recent processor whereas you can usually run 3 years of OSX updates before you need to upgrade hardware - but it was also hardware failures like screens dying or keyboard buttons failing etc..
False economy buying cheap.
We have a three year replacement schedule on hardware. I work at a school so all the computers are budget/low spec and we don't have any issues. We reimage them once every year, which with our deployment system is a doddle to do.