The buxton water temp being reported is from buoy 41025. This is a little bit off the coast and is greatly influenced by the gulf stream.
The water here dropped from 69 to 55 in the last 24 hours on 41025:
http://www.ndbc.noaa.gov/station_page.php?station=41025
Its definitely not always representative of the water at the beach, but there is no closer observation near there.
I would say sometimes the water along the southern OBX could be warmer that Wrightsville area, because of the gulf stream really goes close to the Cape there.