Our pre-school accepts children from 2.5 years, it's attached the the Primary School... so the age range would therefore be 2.5 - 11.
It works well. It's not compulsory. My Eldest wouldn't have been ready for pre-school at 2.5yrs, my youngest certainly was.
I don't really understand that this is not in the best interest of 'the children' in my experience, the children in the school all muddle along rather well, with only passing interest in those children who are considerably older or younger.
I will say that our school has a separate play area for pre-school children, the older children have a lot more room to roam at break time which wouldn't be suitable for very young children.
I think YABU, but I'm not realy sure what your point is.