For a child that is ill, many times they are well enough after a couple of days to do a little bit of homework. A parent is picking up that day's assignments, so not requiring extra work for the teacher, and is bringing the homework back to school when it is due. The so sick that you can't work for an entire week is not that common and a dr's note would already be in place. Most teachers I know are happy to do extra work for something that the student can't help, a serious illness that leaves them incapacitated for a week, but why should parents expect teachers to do extra work putting together homework packages for a parent's whim? A teacher should not be asked to teach a subject twice, a problem that has cropped up quite a bit, parents asking for Johnny to stay in for recess for a review of what was taught during the time they were gone.
I have no problem with parent's taking their children out for vacation. But there are consequences and the parents have to weigh the consequences.
Edited to add: The district my children went to is very, very strict as indicated by my posts. But they were not total monsters. If you could prove that this was the absolute only time you could possibly take a vacation, like military or you are at the bottom of a seniority thing, and that it was not because of cost or just convenience, then they would try to work with you. But it had become a problem that families were jetting off at all different times just because they felt like it and expected the teachers to bend over backwards to accommodate them.