That doesn't mean that they have nothing in common with Mantle.
If you have two different low level API's for the same architecture, there has to be some kind of common code. Also, both the PS4 and XBONE API's were developed with the help from AMD.
Here is the statement from AMD that confirms what I say:
http://community.amd.com/community/...0/17/the-four-core-principles-of-amd-s-mantle
"Similar to" != "Same as."
The difference means they are WORLDS apart. One means they spend no extra money to add support. The other means they spend money to add support. The percentage of users that can benefit is incredibly small. The cost is very likely higher than doing any of a number of other things that would benefit PC gamers (resolution changes, higher quality textures, bindable keys, FOV sliders, etc) and many publishers/developers have difficulty mustering support for those.
If they won't spend the pittance to add a menu for something, I sincerely doubt they are going to suddenly be invested in adding a whole second API just to reach the small percentage of users that would suddenly be able to play the game because of Mantle. Btw, that would be a group of low end users who have not bought an APU yet because Kaveri--the only APU that would benefit--hasn't even been released yet.
So we're talking a very small group that would suddenly be able to game that couldn't before. Other than that, you have the majority of Mantle-capable computers having 7xxx products or later. Again, a ridiculously small group of users compared to the rest of PC gamers that will have older AMD products or ANY Intel/nVidia graphics.
The extra cost won't add enough users to be worthwhile for a great many publishers and there WILL be extra cost because as your link says, Mantle is only "similar to" the code they'd be using for low level access to consoles.
Moreover, PC's have higher resolutions and other assorted differences that would require investment, man hours, support, QA, and patching separate from the DX/OpenGL API.
We're talking so much more money than you guys are allowing for.
1) EA was paid $8 million dollars to support it.
2) Oxide is a new startup who needs cash and/or hardware support.
3) Eidos didn't announce any actual games running Mantle.
4) Star Citizen is supporting everything high end on PC, including Mantle, PhysX, etc.
5) Sweeney is the man behind the Unreal Engine. Sweeney is openly antagonistic toward Mantle. The majority of games that came out last gen and seemingly so far are supporting Unreal Engine or Unity. Unity is unlikely to need the high end performance of Mantle while Unreal Engine is managed by a guy who seems to loathe Mantle.
Two API's costs more to support than one unless that second API is wholly identical to one they're supporting on another platform AND that second API that is WHOLLY identical is 100% applicable to the PC. In both cases, it is not.
So it costs more to support and publishers/developers are trying to cut costs on PC ports, not raise them. There are currently NO Kaveri users who could even suddenly play Mantle games that couldn't play DirectX games and it is unlikely Kaveri will sell the numbers to make that a profitable exercise in the next year. Certainly, Llano, Trinity, and Richland didn't.
Again, Mantle seems unlikely to make an impact beyond perhaps compelling MS to push more Xbone API improvements downwind to PC and getting the OpenGL committee to work harder (re: something Valve is probably already doing).
The most important thing that will compel MS to improve DirectX, however, is actually Valve working on making OpenGL faster than DX. That's going to have the Firefox-on-IE6 effect of waking the sleeping dragon.
Mantle is Opera in this analogy.