Do you really think they are in a position to be picky? You can bet that Microsoft is behind this, in some way. Probably like "how would you like your Windows 10 drivers be delayed in certification if you produce Windows 7 drivers?". AMD needs the Windows 10 for the OEMs to even consider the chips, because -like it or not- Windows 10 is here to stay. The OEMs might want to produce Windows 7 machines, but Microsoft is going to bully them as much as they can. Look at Vista or Windows 8. Even if sales were bad with those operating systems, OEMs had to deliver them. Downgrading was just for select business machines.
Regardless... It is not clear whether those chips won't work at all or just will not deliver all functionality (power management, automatic overclocking, etc...). Newer Intel chips also are only supported on Windows 10, but they're still x86-64 chips, so it should run x86-64 code. I doubt Windows 7 will plainly refuse to run on any of these chips.
Windows 7 is EOL in three years. While I personally think it's one of the best systems made by Microsoft (and I'm a full time Linux user), it's doomed, just like XP was doomed. (Oh, and Vista is EOL next month.... Nobody is sad to see that bastard die, except of course for those people who will now be forced to buy a new machine. Like my neighbours: their machine did what it needed to do, but I expect them to come ring at my door somewhere during April.)