I think much of the bloat or bloated appearance of OS X comes from its Unix background. Rather than wrapping everything in a single file, things like applications usually come in thousands of files once they are localised and contain help. You can see an (over-dramatised) effect of this if you time how long it takes to copy your iTunes application: much longer than copying that amount of data should take. It may sound like a heresy, but the good old resource fork was a way around that kind of problem ;)