Most large PC manufacturers pay a small price for OEM Windows, but then usually only sell PCs with Windows bundled. I prefer Linux, but I get value add also having a dual boot Windows partition.
My suggestion to PC manufacturers: offer an option making the Windows partition only 50% of the disk. This saves some time in setting up dual boot systems. I have used programs to shrink a Windows partition but I would rather not have to do either this or re-install Windows and Linux.