What shoddy writing.
First off, obviously, those numbers in the Apple ad are far from precise - they were rounded to nice clean - and quite large - numbers with several points of precision missing. On that point alone, using them to derive a number as precise as "17.5 cents" is laughable.
Second, as the article itself barely touches on, the download count includes free ads which might be making revenue other ways (iAd) or not revenue-oriented at all. In addition, we have no idea what ratio of the payout was due to IAP via simple app downloads.
Okay, so I guess you could vaguely say that, for every download of an app, something vaguely close to 17.5 cents is generated for a developer somewhere, but that's not really of use to anyone…