Are they? In the mac store? Because the comparison with payment on their own website is kinda irrelevant.
They knew well ahead that Apple would take a 30% cut so I don't understand why some commenters are saying about why this is a "problem."
I'd prefer the money goes to the Document Foundation, who already need to pay to use the app store. It's not a major issue, but it's a downside to the decision in my eyes.