I think you could argue that including a 3d printing api in the os is premature at this point. It could do more harm than good to get in between applications and their target devices when 3d modeling file formats are not yet mature.
A normal user can now download this 3d printing app and make the realization they could print a custom train set for their kid right now on this device with no fuss if they had a OTC 3d printer.
Pretty cool stuff.