Personally I'm with you - I'd rather see rarity values, and the DPG did do away with prices once, actually. But people cried a river over it, so they were put back in. The DP Guide prices and values are just that - a guide. They're not stone tablets from Mount Sinai. As nz17 already mentioned, there's been a dedicated forum here for years for all DPG-related questions and concerns:
http://www.digitpress.com/forum/forumdisplay.php?f=14