> I'm guessing that's just typical Intel behavior requiring constant motherboard updates with almost every tik/tok CPU release?

Yep, but even within the same tik/tok cycle there are different sockets/chipset combinations.

>And... when was the last time Xeon had a 2/4 core?

My point is that most people probably have a desktop motherboard, presumably with a 2/4 core CPU. Upgrading to a used 8 core xeon on ebay is not an option because xeon chips use a different chipset/socket. Therefore the highest available option for most people are 4 core desktop CPUs.