The main issue is, Nvidia have always been full of hype and often lies and they've frequently failed to deliver. Geforce FX, going to be 40% faster than the 9700pro.... late, insanely hot, insanely loud and you know, slower. 480gtx launched only 3 separate times, lies, woodscrews, etc. The ingame streaming was promised a year before it was delivered, or like 8 months, and promised of 2% performance hit when users frequently report way higher.
Nvidia fail to deliver on what they try to, so do AMD, Ati, Intel, and most companies. I have no problem with companies trying to achieve things, if they don't try to do new and better things, we'd all be stuck on a GF3.
As for all these things AMD failed to deliver, I see you consistently talk about them but never name them, funny that. You don't mention AMD putting in loads of effort to create GDDR3/4/5 because the industry didn't have good enough memory, they achieved that, it's the only current reasons you Nvidia GPU's can be as fast as they are.
As for the media hype, developer conferences are JUST THAT, developer conferences, their intended target is not end users AT ALL. The massive majority of all Mantle info was restricted to NDA showings that weren't video'd, conference videos of which some were leaked, and some were released at a later date because people were asking for information.
Backed themselves into a corner, rubbish, complete rubbish, media hype, complete rubbish. The "announcement" of Mantle amounted to a a what 2 hour conference or something in which in the final 5 mins they went "so that's the cards, oh, btw, we're releasing a new API, lols, laters".
Quite some time later again at a developer conference, where it is entirely usual to talk about these things Johan and Oxide talked about Mantle, Johan's main talk was broadcast, Oxide's was not, there were few numbers, little direct information but mostly just talking about how it would work and why it would help developers. This isn't media hype, and neither is people talking about it on the forums. People wanted more information and as such people requested more info and interviews from AMD.
I didn't see AMD claiming anything other than release end of year. As with all things internet now, people take a little information and make up whatever they want. The "release date" amounted to Dice saying they hoped to have it available late december. This was mostly pushed by the usual suspects as a "launch" when it was never billed by anyone to do with AMD as anything regarding a launch. They constant "they're late" was paraded around by people wanting to put a negative spin on everything AMD.
Simple fact is it's an API, this is a huge step and AMD have never held a press event purely for Mantle, nor proclaimed launch dates nor said much of anything to consumers about it. Dev's need to know about what is coming up in the world of developing software, Intel, Nvidia, AMD, ARm all release this kind of information all have these kinds of dev conferences, all telling people what's coming up, how it will benefit them and how to use it. 99% of this information has nothing to do with the end user. AMD have done little to nothing to target or make huge claims about Mantle to end users.
In regards to AMD making all these claims they don't deliver on being a reason to dislike them(yet never list any of them), yet not hating Nvidia for consistently doing the same. Lying flat out often, deceiving almost always with anything to do with Tegra for 5+ years, huge lateness to multiple products which frequently didn't deliver what was promised. I find the hypocrisy.... entertaining.