Well, something fishy is going on because there is literally no way that Safari, in its entirety, is 5.1 MB. The numbers for the others app seem similarly off.

It would be really hard to believe that somehow Apple has found some magic formula to make their apps 100x smaller than Google and Microsoft.

Much more likely is that the reporting by the OS is off somehow (probably most of the app functionality is tied up in shared resources counted towards system files, and not counted towards the app's size).

With respect, I would expect more from articles posted on Hacker News. More thorough research, and in fact an answer to the question.