You're of course referring to PhysX. Now SlowSpyder, I don't know how many times we have to go over my opinion about this, but as it appears so deeply important to you, here it is yet again.
Nvidia owns PhysX, it is theirs to do with what they wish. Disabling PhysX (and NV gave their reasons for this whether you agree with it or not) when an AMD card is present as the graphics renderer, and not an Nvidia card, isn't good from the perspective of a gamer with an AMD card as the primary renderer. Also. Nvidia cards were never ever advertised to work alongside AMD cards. In fact, I don't recall there ever being an advertisement from any vendor in a cards specs to be a dedicated PPU. Only that they HAD PhysX capability. Do you recall anything like that? If you can show me a direct advertisement showing that I'd appreciate it. Like I said, Nvidia owns PhysX. AMD doesn't own 3D abilities as your AMD/Intel 3D HTPC example suggests.
Plain and simply, It's bad for AMD customers who purchased an Nvidia card for the sole purpose of running PhysX alongside their AMD card. But judging from the consensus in this forum about how important PhysX are to them (like worse than liver and onions to most in here) I would count on there being many people who went out and bought an Nvidia card just for PhysX, but more likely just tried to use one of their older PhysX capable cards to try and run it.
In the end, SS, this probably won't ease your mind at all, but it's not just about us. AMD,Nvidia, Intel, all want to make as much money as possible and look for different ways to make their products more desirable. PhysX is but just one way.
Batman AA would be another. I'm sure there will be more in the future.