The point is that you may have a really good app that users want/need, and which presents ads, but in some unobtrusive way that users don't mind.

If you don't put in "anti-ad-circumvention" methods, then the ads will fall victim to some simple blanket blocking scheme that users set up before they even installed your app, not targetting your app specifically.

Analogy: a website with great content and very unobtrusive ads has them filtered by AdBlock anyway.