.....These are specifications that are not controlled by any set formats. Each manufacturer can advertise any number they want. Completely disregard contrast specs for TV's unless they are part of a professional review and have a stated standard for them.
More importantly is to buy a top quality brand of plasma. You will find that they all have plenty of brightness and contrast. In fact unless you have your plasma set up in a pot growing room with huge bright lights (like Stewart's place) you will probably end up with your brightness and contrast settings at or below 50%. The best plasmas have great black levels and super color accuracy.
I recommend looking at Panasonic, Pioneer, NEC, Hitachi, Toshiba and Honda.
I was interested in buying a 50 inch plasma TV but noticed that some have only 3000:1 when most 50 inch plasmas are 10000:1. How much difference does this make?