Are teachers not people? It just seems disrespectful not to at least mention it. I never said don't go. I just said I wouldn't go. Nor would I go without talking to the teacher first as a sign of respect. At least to say hey I understand that you have been working hard the last two weeks on lesson plans, setting up the room and professional development and I understand that that is important and so is the first week but here is our situation. Is there anything I can do to make John's entry into class late go smoother? It's not about priority at all.
Sure they are but mentioning it is not the same as asking permission (which is what you stated before). Why would someone say all of that about lesson plans and yada, yada? If I were a teacher and someone said that to me I would probably laugh and think there was something wrong with them.
I would probably just say "Little Johnny won't be here the first week of school, he's going out of town with family... can I set up an appointment with you for the week after we get home?"