"Death knights are not included at all in the averages. Because they can tank or DPS in any of their specs, there was no way to separate out the tank damage from the DPSer damage. This results in inaccurate numbers, for example showing blood DKs as doing less DPS than even frost mages. While the frost mages are under-represented and we don't know if the numbers are accurate, we know for a fact that the DK numbers are just plain wrong, so they're not included."
Numbers are that low because that's the AVERAGE. Not maximum dps possible, but the AVERAGE.
http://www.engadget.com/2010/05/06/i...lysis-by-spec/