This may be the first time I have ever seen anyone talking about the "neutrality" of D2000. It was (and still is to a point) popular due to its fun coloration. I doubt anyone who did their research bought them because they were closer to neutral than another headphone they were considering.
Edit: Actually I think I misunderstood some of what I read up above. No one said it was neutral, just something about how on the FR graph it looks "more neutral". I will certainly say that the FR graph of D2000 vs. HE-400 looks way different than what you actually hear. The D2000 mids sound a lot more recessed than HE-400 and the D2000 bass feels like there is a ton more than what you see on the graph. Anyway, graphs are dangerous. I ended up getting LCD-2 after looking at that very graph that was posted above, just with LCD-2 added. And D2000 still feels like it has more bass than LCD-2, despite what any graph tells you!
Just to note, where the FR graph sits on the y-axis is totally arbitrary. For example, if you plot the Audeze LCD2/2 vs. HE-400, the LCD's are about 6 dB above the HE-400 in the linear bass-mid range. This is NOT because the LCD's have more bass. This is because the volume that they were measured at is about 6 dB louder than the volume the HE-400's were measured at.