Well, I suppose it's true -- I have submitted apps to Apple that got approved that leaked memory. But the leaks were coming from one of their frameworks (WebKit).
So perhaps what I said should be amended to say: "Your app does not leak memory, at least because of any code you wrote".
It's a worthy goal, but missing it still doesn't cause rejection. BTW, I do include "don't leak memory" in my general-purpose template for testing (as opposed to submitting) iOS apps here: https://ontestpad.com/library/200/ios-app-testing-template
So perhaps what I said should be amended to say: "Your app does not leak memory, at least because of any code you wrote".