Good question! Depending on the model you're referring to the original retail price of a 50" KURO costs more than the price you've indicated above.

In laymen terms, I assume it is safe to use the analogy of comparing a Toyota and a Lexus. Loosely defined, that would mean better build quality, better performance, more bells & whistles, etc....

The main contributing $$$ factor is R&D (manufacturing & development) of the plasma panel  that is produced in-house (other brands outsource). In terms of the 'black' levels, word is that it has a deeper cell structure, filter, high quality glass, etc.

In my own personal observation, the plasma panel is very black when my KURO is turned off compared to my Sammy which is a greyish. There is hardly any reflective light. Deeper black levels = higher contrast and more detailed PQ

There are a lot of comparison made between the KURO and the latest LCD/LED that is available on the Internet. To date, KURO remains the benchmark to beat even though production was ceased awhile back.

Sadly, like all things that is focused purely on quality and not intended for the mass market, Pioneer's KURO achievements also lead to its demise when it is not able to compete in price-point against the overcrowded cheaper HDTV alternatives out there today   

I hope some TV sifu's (I know there's one forumer here  ) can help explain the technical performance of the KURO as compared to the other brands/HDTV alternatives out there. 

Here's a little something to show the difference in black levels



I hope this helps to a certain degree to answer your question