The iPod previous generation iPod Touch is labled as having a Retina display, yet it has poor color gamut and viewing angles (it isn't IPS)
The iPhone 4 had a fairly low gamut display. (And I think the 4s was the same)

I love high pixel density, but I think better viewing angles are even more needed. I'd like to see IPS become the standard like it has for LCD smartphones and tablets.

The HD 3000 is at 4%. All Intel GPU options combined is 10%.
There is just less fragmentation in the Intel market.

The problem is that often the "technical specifications" are meaningless or misleading, like a TV marketed like this:
HD, 600hz, 170 degree viewing angles, 2 ms response time, 1,000,000:1 contrast ratio and over 2 billion colors.

Retina has a useful meaning to me: It means that the PPI has exactly doubled from all the previous products in the line*, while keeping all the GUI elements the same physical size. So it's also a software thing.
No, it's not useful when comparing with other devices, except that Apps made for Apple devices are more likely to target the exact resolution of the screen.

In the case of the MacBook Pro Retina, the longtime standard for notebooks and desktops was doubled (They tend to be close to 100dpi)

Hence the need for a term.

The screen on the Surface is about equivalent to the one on the $399 iPad, though. Of course, all of the specs are different, the Surface may be better in some ways

In some ways, it's worse on OS X. The dock never shows any icons at their native pixel resolution, so they are always less crisp than the same icon in the windows 7 task bar.

The reason for multiple sizes is so elements can be perfectly aligned to the pixel grid for maximum crispness. A vector image won't help in this case. You can lose up to half the effective resolution by not designing for an exact pixel size. Of course, this becomes less important at higher PPI.

There is an x86 Surface that runs full Windows and has a digitizer for pen input. I have a New iPad, but the (ideal) x86 Surface is closer to what I want.

Focus shouldn't be much too much of an issue until the displays are much higher resolution. The push for very high resolutions by smartphones has made this product possible at a low price. One or two display makers recently showed a a prototype of a screen with double the linear resolution of the one used in the Oculus. Beyond that, it may take a long while for even higher resolutions.

When you adjust the focusing lens in this headset, the apparent distance of the screen will be an infinite distance, not centimeteres. With the low resolution of the screen and the small size of human pupils, there shouldn't be any problems with the focus point being different than the convergence point, except perhaps when an object is simulated as being centimeters from your face.

I have more issues with DRM when it restricts my hardware choices, such as DRM for audio, video and books. That DRM limits which devices the media can be used with, such as when iTunes music was limited to iPods and Mac/Windows. On the other hand, I can run Steam on any device that can run the game. For me, the advantages of Steam outweigh the disadvantages of its DRM, except when it comes to the one movie on the service. I won't be buying Indiegame the Movie on Steam, because it restricts my viewing options.

OS X renders fonts more accurately with the trade-off of less sharpness. The sharpness trade-off doesn't matter as much when you double the PPI.

You can set the desktop size to be equivalent to a non-pixel-doubled 1920x1200. It renders the image internally at 3840x2400, then scales it down to the native resolution. Not as good as physically being output at 3840x2400, but it may still look better than native 1920x1200.