Re: Why
Last HP laptop I owned, I took out the Intel wifi card and replaced it with an atheros wifi card - this was a while ago, before intel wrote open source drivers for their wifi. This was simple, both mini pci-e cards, and in a user serviceable hatch on the bottom of the case.
I turned on the laptop, and the HP BIOS wouldn't allow it to boot up with an "unauthorized" wireless adapter installed. I don't buy HP anymore.
I think support might depend on how much you spend. At $JOB we have ~1500 Dell laptops on a 2 year replacement cycle, and about 10 full racks of Dell servers, so at least once a week there was a Dell engineer on-site fixing some issue or other.