You shouldnt expect a BETA to have proper support of old HW is all I'm saying. Once the retail hits, it will be fine. My 4890 doesn't support DX11 either and it works fine in Games.
AMD still supports AGP cards on W7, so HD3000/4000 series cards will be supported in W8, it's a given. It's just not on their priority list right now.
I did say that drivers will probably come after retail like they did last time for 2-3 generations before current gen. Similar issues when they implemented WDDM 1.1.