Socket 939 won't, and neither will early AM2. But yet Core 2 Duo and Core 2 Quads work fine. They lack CMPXCHG16b instruction set, which is a requirement for Windows 8.1 x64 and newer. I can run Windows 8.0 x64 on it or older, or I can run 32bit Windows 8.1 or 10 (11 maybe if I mess with the installer). But it'd have to be 32bit. We're talking early dual cores and quad cores with up to 16, to even 32GB of RAM and more on the dual and quad socket boards.
Granted those systems won't play MODERN games, but there's still a ton of games even on Steam itself that have Windows XP or even 98 as the minimum requirement. Or even Windows 7, thousands probably for 7. By knocking out support completely, its almost forcing users into TPM and upgrading, just to play games that they paid for. That's my complaint.
And yes, the Chrome underbelly of Steam is absolutely the problem here, agreed completely. My original point was, they COULD release a library ONLY version of the client to allow vintage systems to still access games that were once played on them (including Windows 7 systems now). No social part, no store, no community pages, just a download and play option (or even just a downloader with a steam login to access the games). They COULD. I'm not saying they will, clearly that's a pipe dream and will never happen.
Here's an article from when 8.1 was released that goes over it.
http://www.pcworld.com/article/2058683/new-windows-8-1-requirements-strand-some-users-on-windows-8.html