Good chart! But for those that don't know about it, this chart represents the portable side of things. There are sub hundred dollar devices(like i river) and a few others along the range(albeit not very known) that can and has lisencing ability to bypass the iPod or iOS devices own DAC and amp , although they are desktop use which at that point in my case..would be redundant for my use.
Not to knock on WiR3D, as this chart is a good starting point, but it's also somewhat simplified. e.g. to me. There are a few points of which I may not necessarily agree with the chart (e.g. I personally wouldn't consider the iPhone's DAC to be a "good internal DAC", & in the Android world, none are official DAC/Amp supported (will see when JB 4.1 actually open to the greater public).
So far, I've not come across many USB DAC/Amp portables that I like. I personally haven't been impressed iBasso D-Zero, almost all of Fiio range (except E17, they may have something there), and even the RSA Predator (average DAC but great Amp).
IMHO, for now, the iDevice DAC/Amps have more of an edge over Android are more mature and currently the real competitors to the iDevice DAC/Amps are the DAPs (Sony NW-Z, iBasso DX100, Studio-V, etc) but most of the DAPs have UI challenges.
Once Android's JB 4.1 is in production, then I'm guessing a new range of USB DAC/Amps will appear to raise the bar to be competitive with the iDevice DAC/Amps.
P.S. note that I'm referring specifically to DAC/Amps. Amp-only would be an entirely new topic.