Not to be mean but if you struggle with understanding what an open standard is, how can you call someone on not understanding the highly technical side of the underpinnings of Mantle and how hardware or drivers would be developed to support it?Because AMD could just change Mantle, and then Nvidia's implementation would have to be redesigned. That's why they don't give it a shot. It's not worth the risk. AMD specifically said it is controlling Mantle so it can better optimize its own hardware. What part of this makes it hard to understand why Nvidia doesn't want to touch it?
One seems a lot more complicated and not being EA or AMD one would be hard pressed to be able to pinpoint what implementation would really mean for Nvidia. The other one is a simple phrase with a given value within the context of the thread that is understood by most people.
For all you know Mantle's implementation for Nvidia and their processing units would just be a couple of driver hooks. Remember that Nvidia's unit are still larger and more complicated than AMD's (which is why AMD units end up being better miner GPU's) so it's unlikely GCN could easily do something that Kempler can't. There are a lot of decent reasons for Nvidia not implementing Mantle. But hardware development paths might not be one of them. The simplest and probably more correct statement would be to develop a Mantle driver would mean lending credence to the API, which in turn would push adoption, which in turn would give AMD more clout in the evolution of PC Gaming graphics. They wouldn't want that.