Best Argument: Impossible
What's best for the students
I understand that many people have an aversion to Apple products, but they need to set that aside and look at what is best for the students. Android has not shown that an open ecosystem is that beneficial -- with inconsistent experiences and content experiences that range from good to bad. Closed ecosystems generally result in more consistent products that can be easily managed with minimal staff.
Apple has made the iBooks Author tool simple to use and free so teachers who want to offer up customized experiences and tools are free to do so. When teachers create outstanding resources, they can easily share these throughout the country and know that others are able to use and take advantage of their work because the ecosystem is standard across the entire educational sector.
Cost is a factor, but let's all step up to the plate and make education the priority.
Open and cheaper alternatives
There aren’t many people who aren’t utterly enamored of their iPads. But guess what, folks? There are alternatives. Apple will make plenty of money in education, but the iPad will not become the de facto choice for the “tablet in every backpack”.
As we’ve seen with Windows marketshare in education, no matter what sort of discounts or market positioning Apple applies to the iPad 2 when it launches the iPad 3 (think white MacBook), there will always be cheaper alternatives that meet the needs of students as well as the iPad and that don’t require buy-in to a closed ecosystem. Apple threw down the gauntlet with iBooks and iBooks Author and made it abundantly clear that for educational content on the iPad, it was the Apple way or the highway. While this will work for some settings, most will gravitate towards more open (and cheaper) solutions.
Budget realities and impossible dreams
When we look at tablets for education, Apple is off to a running start with the iPad and interactive books, and this is likely to get Apple back into the education market and shape the education industry in the years ahead. Matt is absolutely correct that the Apple approach offers a simple, unified experience that a lot of schools and school systems are going to embrace.
Still, it's unlikely to become a universal standard. There is already a strong open source bent in a lot of the education sector and a lot of well-funded companies from Intel to OLPC want to continue to feed that. Budget realities will also drive a lot of educational institutions away from Apple and toward low-cost alternatives. So, Chris is ultimately correct that an iPad in every backpack is an impossible dream.