That doesn't really work though. It's a pretty apples to oranges comparison. For a desktop PC it's entirely possible to re-use peripherals from the last desktop PC, even the monitor can be reused. A laptop is a single unit, once you retire it, you retire ALL of it. Also a LOT of desktop PCs are actually sold with nearly everything in the box except a monitor. Keyboard, mouse, even speakers.
And then their use cases are different, again, I'm stressing portability here.
Desktops to laptops is, simply, a largely apples to oranges comparison.