The reason that the schools set a strict attendance policy of how many days can be missed is strictly FINANCIAL! They don't give a rat's behind how your child is doing in their classes. They lose money for every day your child is out of school. The district loses money. Your child = $$$ , plain and simple.
So to make sure they can cover their budget they put in place a whole lot of scare tactics-- truancy officers, threat of retention, no credit for assignments etc. If they truly cared about the kids and thier educational needs they would provide the work needed before or after an absence and allow them to make it up at full credit. They would realize that as long as the kids have passing grades then there is no reason to retain them. ( in my district parents have the right to overrule a retention decision)
I was in a classroom with a kid that was a chronic truancy problem. He refused to come to school and mom wouldn't make him. The schools know good and well which kids are really truancy problems and which ones have involved parents that have education at the top of the priority list. When they start threatening with these types of consequenses is when I think parents need to stand up for their rights to actually be parents and make the decisions for their kids, and not let the schools bully them.
Now keep in mind that I was a public school teacher, am currently a sub for our district, and am very active in the PTA. I support the public schools and public education. But my family and children are my top priority. And I also did homeschool for several years and wouldn't hesitate to do it again if I felt I had to.
Every family has to decide for themselves what they are willing to put up with in order for their kids to miss school. Me, I would do it in a heartbeat, tell the school exactly what I did in that note and be done with it.