They're almost lying.

By definition, image contrast is the difference between the amount of light coming from a "black" patch, and that coming from a "white" one. If there's no ambient light, then an OLED display *may* have infinite contrast in an ideal world, but in the real world it doesn't (like all LEDs, OLEDs emit a tiny, tiny amount of light in their "off" state).

Add ambient lighting, and the screen material comes into play. Now the "black" level depends on the amount of ambient light reflected back off the screen. Use a glossy screen, and you can redistribute this reflection, to make it look better when shadowed by the viewer (like in a shop, for instance), but you're only rearranging the problem, not solving it. [I'm typing this on a glossy-screened Apple product, with just such a stupid shiny screen, and I absolutely hate the display.]

Other manufactures using LED/OLED just quote insane contrast ratios, like 10,000,000:1, which are about right for an OLED panel.

Also, the reason for the fourth, white pixel is that this is most likely to be a Pentile display matrix (not the same one as used in phone panels). Here, the large white subpixel deals with the baseline illumination of the whole pixel, with the RGB trio there to colour it. A true RGB set gives better colour reproduction, but is susceptible to more noticable colour shift as the cells age.

I remember the first plasma sets coming in at this price, but then, they were competing against CRTs, which were utterly impractical at sizes over 30". Still, we have to start somewhere -- I'll look at them when my LCD set needs to be replaced, in about seven or eight years.