Are you guys joking?
You're looking at data for the #1 free app in the store and the free top 50, which represent the top 99.8 percentile in downloads. So they're telling you that if you're in the top 99.8 percentile, ad based software can be profitable. That is not a strong statement.
The real reason developers use ads in their apps is not to generate revenue, but simply to upsell the paid version of the application. This will become more and more prominent of a method because Apple has disallowed developers from advertising features of the full version in the free version of their apps. With ad based applications it's obvious what features are in the full version -- there are simply no ads.
Let's go through a little calculation. I have a relatively popular iPhone app with free version and a paid version. In the past two months I have made about $2000 in sales (which is hardly a huge success, but these numbers are actually above average). I gather statistical data from the app, and from this I know I have about 10,000 users that have played 200,000 games.
How much money would I have made from advertising in the free app? According to Ad Whirls data I can make up to $1.00 per eCPM. They don't state in their .pdf how refreshing the ads affects the eCPM, just that it lowers it, so I'll assume no ad refresh here. So lets assume 1 impression per game ... that would give us a total of 200 eCPMs, for a grand total ad revenue of $200.
Moreover, the $200 estimate assumes that the free app with ads would be as popular as the free app without ads. But this is not the case ... many users would have never downloaded the app in the first place or would have stopped using it due to the ads presence.
So, as a developer, would this have been worth the time it would have taken for me to redesign my app to incorporate ads, and to program them in? Absolutely not.
To conclude here, this story is not news -- it's propaganda from an ad company.