It's normal.
I thought that my Dakota 20 was not as accurate as my old Etrex H. However when I tried to compare them they were just different! Neither was more accurate but they did give different readings if that makes any sense.
The Dakota, even if it were an extra 15ft out which it isn't, would still be the better unit for Geocaching though. Combined with GSAK and a Premium Membership it gives as much information as I need as well as navigating me to the correct spot.
My HTC Desire HD gives even clearer information, although not as accurate as a GPSr, and for most caches is more than adequate.
I guess I just love Geocaching!!