I wouldn't trust that review entirely, for 2 reasons.
They test black level after turning off both the ambient sensor and the Led Dymanic control, the later is important for the screen uniformity. They even calibrate it for 100% backlight.
They tested the 46NX720 and had similar results with black level and uniformity, but they mentioned under Viewing Control the following:
"Sony tucked away a really awesome feature: LED local dimming. For those of you who aren’t familiar with this feature, if you have an LED backlight, it’s possible to program the TV to dim or brighten each light-emitting diode depending on the picture in front of it, boosting the effective contrast of the picture without actually changing the performance or programming of the TV. It’s not perfect, as it can lag a little bit from time to time, but it is pretty cool to mess around with if you want an even wider contrast ratio.
When we enabled the LED Dynamic Control setting in our tests, the KDL-46NX720’s contrast ratio exploded, giving us a deepest black of 0.01 cd/m2, and a peak brightness of 311.13 cd/m2, for a total contrast ratio of 31113:1. "
Yet they fail to mention this in the review of the HX820, this Panel is designed to have its Led Dynamic control enabled and will give its lowest black level and best picture quality with it enabled. Turning it off is fine for testing as long as you also test and report findings with it enabled, which they didn't do.
Anyhow I have a 55HX820 and I absolutely love it.