No, these are all correct! And your own explanation is a good one. In English, you will often see exclamations of disbelief or awe (e.g., "You worked until dawn?"), or challenges and reaffirmations of fact ("You work for me, don't you?"), phrased with a question mark like this. This is done when the speaker DOES NOT EXPECT AN ANSWER or when the answer is obvious. It isn't really a question. We already know the answer. These are called "rhetorical questions" -- questions to which we don't need or expect an answer. Some look like regular questions, but they aren't. "Do I look like an idiot to you?" "Do you think money grows on trees?" You will also see sentences that LOOK like questions ended with an exclamation mark: "Did you get drunk again!" "How could you steal from me!" These are really an exclamations that happen to be phrased as questions. And again, the key is that we don't expect an answer. All of these are correct English grammar. I will mention that the use of multiple punctuation marks (?!, ???, !!!) is NOT correct English mechanics; but it is acceptable in colloquial writing (Internet, personal letters, novels, etc.).