True. There are also things like UFS fragments and ReiserFS tail packing etc, but does plain ext3 or ext4 implement any of these optimizations? I don't think so. So in the most common case nothing is gained by this optimization.
As this has been discussed for quite some time, I actually thought it was already enabled in ext4 -- apparently not.
BTRFS supports "space efficient packing of small files" - by suballocating blocks. Not sure what the real mimimum size on disk for a file is though -- but apparently you can approach header+<data> size both on btrfs and ext4 (and on BSD under UFS2 afaik).
