Mainly because I currently have a GigaByte board that currently runs an overclocked Slot A 650 (can only get it to 715 because anything higher and it won't even POST) and it's been working flawlessly since Day One.
My current fascination is an older [link|http://www.giga-byte.com/products/7vrxp.htm|GA-7VRXP] and possibly an XP 2000+. Yes, the board is a bit dated, but a) I don't want Bleeding Edge, b) the onboard NIC and sound have a prayer of working with OS/2 Warp 4, and c) the prices for it are coming down as vendors are unloading excess inventory that hasn't sold.