it isnt poor business practices, but it also isnt AMDs fault of not using Physx. Nvidia bought Physx for themselves some years ago. they really dont have to share it with anybody. but as far as this decision of wanting to include physx in ps4, it seems kind of desperate of Nvidia. they were left out of this console gen(also reason I think they created shield) and they want to have at least some bragging rights in this gen.
It is when the head of AMD/ATi's graphic marketing department says we don't want or need PhysX because we are developing our own physics API.