The sibling posts may have forgotten about laptop variants like the i386SL, i486SL, and the IBM 386SLC and 486SLC. These were lower voltage, lower power, and included power management features that weren't present in the mainstream SX/DX chips. There were cmos variants of earlier chips as well that used less power too.

That doesn't mean all laptops used these, I'm sure some laptops used desktop chips.