support for another cpu includes different motherboard and its component bugs including base chipset, mb integrated peripherals, bios and drivers. most vendors support these things for 2-3 years after introduction.
it's a big deal when your margins are dependent on no calls.
why do you think oems prefer "universal" motherboards?
CPU needs no service or support. Anyway, much less than a floppy, hard drive or a power supply, and Dell swaps these freely.
Really, I guess you don't believe a CPU comes with its own chipset and platform base. Stop thinking like a tech junky and think like an OEM that has to supply customer support for a platform based on a chipset and CPU.