This comparison might not seem fair, since many options available in the standard tools are not available in the busybox, but the essence is that you can pack lots of functionality into a tiny executable, if reduced to the minimum needs of administration. The real challenge is deciding precisely what is needed and what can be removed. With all the dependencies within an OS like Linux (and the use of shell-scripts for many jobs), this is not easily decided. This leads us back to one of the motivations for such a minimum system: reduced system complexity, which eases understanding of such dependencies.
The second comparison is the hello world program in C compiled with gcc (egcs-2.91.66) as an ELF-executable and the size difference of a hello world function added to busybox called via a link named hello. The ELF-executable comes in at 33KB raw and 7KB stripped. The increase in size of the busybox, however, is a nominal 161 bytes.
This shows how efficiently the overhead reduction is achieved by having one main routine and calling everything else as a function, via the name of which busybox is called.