And yes, models without Windows are typically cheaper, sometimes significantly.
Consider ProBook 450 G3 X0P36ES versus T6Q45ET. They both have i5-6200U, 4GB RAM, matte 15” FullHD, Intel GPU. The former has FreeDOS preinstalled and costs €540, the latter includes Windows 7 Professional and costs €750.
I bought then an ASUS n46vm with win8, hoping to remove it and install linux... never figured how to boot any os installer, even after disabling secureboot even memtest86 refused to boot.
Manufacturers pay the distributions to do hardware enablement if they think there is a customer for the OS on their hardware: alternative OS users are invisible if they buy Windows laptops. Every quarter when the distributions meet with the manufacturers the main topic of conversation is how many units shipped with their OS - this guides investment.
Furthermore, manufacturers are the main way that other parts of the ecosystem learn about demand for an OS. As a Linux distribution, if you can't get Intel to give support for a chipset then the main thing you do is phone up HP/Dell/Lenovo etc and get them to convince Intel for you. That's not going to happen if the manufacturer doesn't know that there are client side Linux users.
[0] I don't know about the hardware enablement story for alternatives like *BSD
Can you actually get these *nix laptops for cheaper than their Windows equivalents? I personally consider Windows these days to be just one more piece of bloatware to remove, but I never got the impression that it added much to the bottom line cost.