The pair scooped the 2011 title, following on from previous winners including last year's duo Fiona Bruce and Ricky Whittle.
TV presenter Vorderman, 50, managed to fight off strong competition from Pippa Middleton, who attracted a large number of votes after the royal wedding.
"I am really surprised and flattered to get this award, particularly at this stage of my life," the former Countdown host said. "I always suspected there were a lot of people out there who were glad to see the back of me, so this has turned out to be very funny indeed."
Middleton was "totally unknown" prior to her sister Kate's marriage to Prince William in April, said organiser Tony Edwards.
"There have been quite a lot of votes for her over the period after the royal wedding, but it was less than six weeks from then to now and a lot of other stars had a lot of time to really ratchet up the votes," he said. "There is no doubt that Carol Vorderman has got many, many more votes.
"The bottom line, if you want to use that expression, is that if you Google Carol Vorderman's bottom and stand back, there is a mass of websites dedicated to her rear assets."
Meanwhile, Strictly Come Dancing star Du Beke said that the accolade was an "absolute honour".
"Sadly, it has often been said that my rear is better than my front, so thank you very much indeed," he said.
> 'Rear of the Year': The award-winning celebrity bums in pictures