I'm a high school physics teacher and this is something of a pet peeve of mine. While I am sympathetic to the costs of traveling during school vacations, the burden of making up the work tends to fall on the teacher. This is particularly true in science where labs (which are required in my state and for AP courses) are not easy to make up in terms of equipment and in the case of chemistry, without substantial prep work. Now you may be saying "oh poor teacher with summers off complaining about having to work." I just say, if you want me to bear the same, if not more of the burden of catching your kid up, you have to take me to Disney with you.
Also, there is a reason why we have 20 kids in a class and its not because they learn better that way. Whether we want to admit it or not, education is a volume business. We work hard to make sure we reach as many kids based on learning styles, disabilities or just personally as we can, but as Spock said, "the needs of the many outweigh the needs of the few."
On a side note, I believe the consistent removal of students from school for leisure activities sets a bad example that makes their time at school much more difficult as you are basically telling them that school really isn't all that important. Then they go to college and expect the same level of accommodations and can't handle it when the professor tells them, "too bad."