I've just had a little chance to test a few Windows 8(.0) Pro Tablets with default factory setup, this might help to know the devs.
Sony Vaio Duo 11 (i5) (Well, as Vaio Duo are actually UltraBooks and has better Gfx card, but running GLView shows it doesn't fully support 3.0)
Sony Vaio Duo 13 (i5)
Acer Iconia W510 (Z2760)
Acer Iconia W3 810 (Z2760)
Asus ViVoTab ME400c (Z2760)
Lenovo Miix 10 (Z2760)
Some are bought by me, some are from my friends.
It seems these models are only OpneGL 2.1 capable(default), and has Shader model 3 support.
DX9 is not present by default, you have to manually install it.
I can't determine is Windows 8 or integrated Intel Gfx chip limited this, but at least I know in Enigma,
OpenGL 1 mode will work well(installed and tried).
Windows 8.1 Tablets are coming, but I think the driver is about the same, if you're trying to distribute your game to NetBooks users, you may have to meet the requirements.