Wouldn’t that „test“ imply that Apple isn‘t doing any kind of marketing/promotions through the 30% cut? At least here in Germany, discounts and boni of 10-15% when buying iTunes gift cards are quite frequent. And these discounts influence at least my app buying behavior. In addition, these discount offers are advertised and so indirectly promote the App Store to millions of people. Developers profit from this in one way or the other.

In your test just cutting the 30% „Apple tax“, the developer would still profit from these discounted gift cards. But it’s not the developer giving the discount from his cut, but Apple from the 30%. Moreover, the 30% covers not only handling and processing App Store Infrastructure and sales, but as well the editorial sections of the App Store promoting news apps daily. There already exist reports on how this editorial content boosts app sales.

So, your test would still take all this for granted and therefore would be highly skewed. The data would not be „statistically significant“ at all.

I never said Apple doesn't do anything for their 30%, and I make no judgements about whether it's warranted. My comment was just a thought experiment about how a law firm might approach making a case for damages, given the conversation people were having.

You may buy iTunes cards. I've never bought them, nor even looked at them. I don't know which of us is more representative, but I don't think that invalidates the broad strokes of a test like I describe.

"A law firm could easily pay a number of app makers to try this out in exchange for the data, and then make a huge class action out of this."

I'm not sure you really want law firms doing this. The recent practice of people investing into litigation has not exactly done wonders for anyone.

I don't want it, just saying that it could probably be done.