"Legal" is not the same as "good idea" or "immune from criticism".
Even if Apple is predictably bad about this, each instance of them bringing the hammer down is still a surprise, because that's the nature of the problem.
People spend a lot of time developing applications, and Apple will very inconsistently cause all their efforts to be wasted.
Developing a calculator that sits in the NOTIFICATION area of an OS does not strike me as thought out. Especially seeing as how gigantic this particular one is.
Is it surprising to you that Apple has an issue with an app that makes a mockery out of their notification center by completely obscuring literally every notification in there?
And here I thought devs were smart enough to read "Notification Center with widget ability" and figure "Well, I guess I could put a notification widget in there" and not "Ooh, sweet. that's where my calculator goes"