I'm sure that this will be an unpopular opinion with the loudest Mac Rumors users. However, as a developer of one of the most popular social apps in the App Store, I completely agree with Apple doing this. The apps asking for tips say that Apple does nothing, however, those same apps would be nothing without the App Store. Apple takes care of some marketing, distribution (including bandwidth and storage), moderation, oh, and, let's not forget, the frameworks and tools that make it so easy to develop for the Apple ecosystem.
Developers asking for tips through the app are purposefully bypassing the mechanisms meant for this type of thing, in an effort to stop paying Apple. This not only gives them a leg up on the competition, it also bypasses protections that Apple provides to the consumer.
This is the equivalent to an illegal worker taking cash under the table to hide income from the IRS, while still using all of the public services that our tax dollars provide (like public parks, roads, police, fire, etc.). Then, screaming that they shouldn't have to pay taxes because the government didn't do the work. Disclaimer: I'm all for small government, it was just the most relevant example.