[Haskell-cafe] Why doesn't GHC use the Hugs definition of splitAt to avoid traversing the first part of the list twice?

I've just been investigating a performance oddity in using splitAt on a long stream of random numbers. I don't understand why GHC appears to want to traverse the first part of the list twice. GHC seems to implement the splitAt function something like splitAt n xs = (take n xs, drop n xs) whereas Hugs is something like splitAt n (x : xs) = (x : xs', xs'') where (xs', xs'') = splitAt (n-1) xs which seems much more sensible to me. Wouldn't it be better to change GHC to the Hugs method? Have I misunderstood something? Richard.