The decision to pick Wade over Haddin was not a straight forward one. Haddin has already proven himself as a good tactician and a far more attacking batsman.
Haddins strike rate:
Wade's strike rate:
I guess age didn't help Haddin's case. There is an interesting article on Cricinfo about the selection decision:
" Haddin remains a strong chance of going to England as the back-up wicketkeeper and a senior member of the touring squad. His experience of England and personal success on the 2009 tour would be a useful asset to the tourists, especially given some of Wade's struggles while taking the gloves in the 4-0 ODI series defeat Australia suffered in June and July. Wicketkeeping in England requires an awareness of certain subtleties, like the ball's tendency to move in the air after it has passed the bat, and Haddin adapted far better to them on his visits to the other side of the world than Wade did this year. Even if Wade retains the gloves throughout the tour, Haddin's advice and intensity as a training partner would be highly useful."