I believe that with ext2, small short-lived files only ever do exist in memory, just as you suggest. Few people store '/' on ext2 these days.
With journalling things become a bit more complex. You need to ensure that the various metadata are journalled in the right order and by far the easiest way to do that it to place every updated block in the "next" transaction. So with ext3 journalling (if I understand it correctly), every metadata block that gets changed will be written to the journal on the next journal commit, and then to the filesystem.
A filesystem which does delayed allocation would be better placed to optimise out short lived files completely and maybe ext4/xfs/btrfs do better at this. However I suspect is it far from trivial to optimise out *all* storage updates for short-lived files and I doubt it is something that fs developers optimise for.
So I think that you probably could see it as a filesystem problem, but I'm not sure that seeing it that way would lead to the best solution (but if some fs developers see this as a challenge and prove me wrong, I won't complain).