It's a tricky one with keepers I think, because they could go throughout an entire game without having a single shot to save. So a clean sheet is not necessarily down to the keeper.
Players can miss absolute sitters from a goalkeeping error can't they, so it's quite had to quantify I feel.
Also, then you have to factor in goals that HAVE been down to the keeper too don't you. A keeper could let in 5 goals and not be at fault for any of them and then by the same token, could let in 2 and be responsible for both.
Be interesting to know of those clean sheets, how many were down the defence, the ineptitude of the attackers and how many to the keeper helping keep the team in the game.
Stats can be very useful at times, but are can also be governed by interpretation.
I don't think anyone has said Wilson is a very good keeper have they, but if you looked at that stat above, it would kind of point out that he IS a good keeper wouldn't it.