The more telling statistics for a wicket keeper in the field are the number of dropped catches and missed stumpings per match. In the professional game, you would expect the wicketkeeper to catch all but the most difficult chances, and to cleanly gather the ball and attempt a stumping whenever possible.
An example of this is when the England wicketkeeper Matt Prior was dropped for the series against New Zealand in 2008. The explanation by the Chairman of selectors was
the selectors feel that he needs to further improve his wicket-keeping in order to realise his full potential in international cricket.
but the more telling explanation was from the BBC cricket expert and former fast bowler Jonathan Agnew:
It's harsh but fair on Matt... he simply dropped too many catches.
I couldn't find any statistics on drops by wicketkeepers. Maybe the coaches keep statistics, but in doubt you can always ask the bowlers, who don't forget drops too quickly.