There appears to be an "error" in the packaging/zipping process of the Mac OS X version of Arduino. After further investigation, what should be symbolic links are being replaced with the original file/directory. "tools->avr->avr" should be a symbolic link to either the avr-3 or avr-4 directory. Instead it contains a duplicate copy of the avr-4 directory. Similarly links in "tools->avr->bin" have been replaced with the originals.
Correcting this will reduce the Mac OS X Arduino download zip by 25MB. :o
I was also able to find out that the reason why there is both avr-3 and avr-4 included is because gcc 3 is purported to produce smaller output than gcc 4 in some situations.