I don't forget that they pay for it, I just think it's so tiny as to not matter in this discussion.

Downloads are such an infinitesimally small cost, relatively speaking. I don't have comparable download numbers to the Apple store, but I do help maintain software that has 3+ million downloads a year (and it's a quite large download, too, compared to mobile apps, at 15MB). The cost of hosting those downloads and the bandwidth for them wouldn't even really be a blip on our radar in terms of costs of running our business and projects. Bandwidth is cheap these days. Hardware is cheap these days. And, it takes almost no hardware to serve file downloads. We've had people offer to provide mirrors for us for free, but we don't take them up on it (though we can't stop people, either, being Open Source) because we'd rather have the data about downloads than the tiny savings in bandwidth and hardware.

What's a few hundred terabytes a year of transfer and storage for apps to an organization like Apple, that also serves out millions of HD movies? It is closer to "nothing" than it is to "something".