DD misses nursery occasionally, for a good reason, like family visiting, trips away when we cant do other times.
Family holiday time away is as importan as education, it helps to create family unity, continue developing family bonds, learn new experiences etc etc.
Going on holiday during holiday time is very expensive, and can make the difference between going and not going, for some families. I think while its not good to continually disrupt a child's educational routine, going on holiday once a year, or maybe even twice a year, and missing nursery is really no big deal.
This age is far too young to be so formal and strict about schooling.
I think though it is personal choice. If you are in a position to have your holidays in the official holiday breaks, that is a choice you make, and you are not unreasonable for that decision.
YABU to think less of a friend for not choosing to do this with her children.