So yeah, they want control of the developer platform; eliminating the distinction between Windows 8 games and Xbox games would make development more difficult. You could argue that they could get that control by intensely curating the store, but the problem with doing that is… Windows PC hardware isn’t homogeneous. The Xbox’s main virtue is that it provides a consistent hardware platform for devs to work with; all x86 games don’t follow those same requirements. It would require a massive porting effort to make the effort work. Furthermore, who would play all those games? There’s not an intense market for the back catalog of x86 games in the Windows 8 Store; I can’t think of… any games on there that would make the effort worth it.