One advantage to paper textbooks and handouts is that it can be taken home, where the parents can see it.
With an iPad or similar device, the school could control what material is stored locally on the device, and what is only available from the school's wireless network, preventing parents from seeing "controversial" content, but still making it readily available to the students while they're at school.
Unfortunately, it’s been my experience since my 10 y/o started going to school that schools here no longer allow students to take textbooks out of the classroom, no doubt because of their EXTREMELY high costs and the fact that parents were not responsible for the missing/lost/destroyed/stolen textbooks their kids were assigned in the ‘old days’, and handouts tend to get tossed in the trash when my child cleans out her backpack -I do check them out before that, but how many parents really don’t worry about going over their child’s handouts?