The difference between calibrating by software (GFX LUT calibration) and hardware calibration (monitor LUT calibration) is large in theory. In practical terms, people won't notice, since they have no reference point.
The theory is this:
The screen is 8-bit per RGB. The colors are mapped within the screen itself in the monitor LUT (lookup table). This gives 256 colors for red, 256 colors for green and 256 colors for blue (256x256x256=16,7M colors).
Lets say you wish to adjust the white point. The white point is a mixture of red, green and blue. As mentioned, you have a range of 0-256 for each primary color.
When you adjust it in GFX lut, there is a compensation going on. In effect, you are reducing the range of your primaries to get the "proper mix for given white point). This is because the monitor LUT remains the same (same white point, same range).
When you adjust it in the monitor LUT, you are changing the screen itself with no compensation going on. You preserve the color range.
The NEC's have 12-bit lut and 12-bit gamma correction to ensure that you get smooth stepping without banding also after calibraton.
In additon, if you calibrate with colorcomp on, it will even out the brightness, so that the colors are even across the display. As you might or might not know, colors are usually not uniform across a display. You can calibrate it to a perfect DeltaE level in center, while 5cm left it will be a totally another story.
Here's an illustration:
Before colorcomp:
After colorcomp:
http://www.prad.de/en/monitore/review/2007/review-nec-lcd2690wuxi-part9.html#Image
Note that this has nothing to do with the uniformity of black, but the uniformity of the colors. So you cannot measure or see it with a totally black screen. 155 is 155 cdm2, which means brightness, not black level/black depth.
If you wish to buy Spectraview 2, you need to transfer money to your US relatives (or receive it from an uncle in america as in monopoly). This is because they have blocked EU creditcards so we cannot buy it. Then they need to send you the serial and you can download the program from NEC's homepage in USA.
Just install it with the key and you are set to go (and you don't have to press any buttons on the screen to do so ;) ).