From what I've read repeatedly, DirectX 10 in RE5 was only necessary for NVIDIA 3D Vision to work. The game had no other DX10 features. I'm not even sure if any Capcom games on MT Framework use anything other than DX9; going by the recommended specs for Revelations 2, that game is still only a DX9 game.
I've played through RE5 numerous times in DX10 mode and can't tell a difference between DX9 mode.
I'm not sure that the removal of DX10 needs to be a key point or at least it could be put in with the 3D Vision point.