Wow, this thread took a turn from the title!
I agree with the principle that there is no point having a policy which is not enforced, especially when the policy is there for good reason.
I also see parents at our pre-school who will send their DC in regardless of illness until the school sends them home. This isn't just D&V, it's everything from colds to flu to hfmd and chicken pox if people can get away with it.
We seem to have developed some kind of idea of entitlement that schools and teachers are their to provide childcare whatever the circumstances rather than remembering we are ultimately responsible for our children, even if it is at the expense of a days work / fees lost. However this approach also seems to have been fairly widely accepted so we have to acknowledge changing expectations.
personally think this is not just difficult for the poor kids who are ill, but it's often also irresponsible as in OPs case. You never know someone else's circumstances. I now feel that if we have something big coming up like a holiday, wedding etc, I have to actively keep DC away from other kids for a few days to stop them getting ill rather than being able to expect another parent to keep their ill DC away from everyone else.
However, OP, it does sound like you have a very complicated and demanding situation. Tbh, I think your point about enforcing policy is not unreasonable, but I just don't think any policy in the world would be enough to protect a family of six people with differing health issues from some disruption or difficulties due to school absences. I don't think I could have had so many children in your situation, I would have been exhausted with one or two!!
Overall, your point is not unreasonable but your circumstances are an exception, not a norm.