du -s excluding size from directory entries?

[Aaron Davies]

is there an easy way to `du -s' a tree and ignore the size of the directories 
themselves?

if, e.g., i have one deep directory tree with a long history of modifications, 
and another directory tree created from a `cp -a' of the first, their `du -sb' 
results are likely to be somewhat different.

i can get this result with something like `find -not -type d -print0|xargs -r0 
stat -c %s|paste -sd+|bc', but a simpler solution would be nice.
-- 
Aaron Davies
address@hidden