Official speculate before its too late: RSX Spec thread

[DeanoC]

DX is just a software layer, nothing to do with the HW as such. The HW has to be able to perform certain set of functions, but that's got nothing to do with DirectX as such. Just like all our gfx cards can also run with OpenGL, which is totally different than DX. Maybe some shady "DX-only" features might be removed, although I doubt it.

Actually that not strictly true... Direct3D and OpenGL differ on some definations, that are actually embedded in the fixed function hardware (the example I can think of if viewport depth defination (0-1 or -1to1) ).
As such consoles chips with a PC heritage hardware often have a 'API' flag in hardware. Usually its left in as its such a minor peice of silicon.