Again I don't mean to dump on Google who is at least trying to address the market. But they did so without asking what the market actually needs/wants or looking at what smart schools are currently using (and the related costs)
However, like you said, the usefulness of Chrome OS for students is definitely debatable. In a few years, a web-app only classroom might be more viable, but right now, it doesn't seem too practical. Plus, a tablet form factor seems more useful than laptops for classroom use.
For the record the 4 year is based on using that brand for some time. They actually can go about 4.5 years but after 4 years we consider them a loss. I can't imagine Chromebooks are going to be replaced more often than every few years.
On the Asus even if a few break (and it happens) the cost is spread over all the rest making it negligible (less than $.75 a month in my experience)
I am assuming that you are not using a payment plan to buy your netbooks, and are actually purchasing them all upfront.
Though another issue is with the Google Chromebooks you have to sign up for a 3 year contract (though you obviously wouldn't have known that when you made your initial comment): http://searchengineland.com/google-chromebooks-out-june-15-3.... So on being able to change course that's not as possible as it seemed when you made your comment.
As far as Elementary Education vs. Higher Learning I would be surprised if this took hold in Universities. The only advantage I could see is cost for students and with studies showing 70% of College Freshman having Macs (http://osxdaily.com/2010/08/05/70-of-college-freshman-use-ma...) I don't see kids settling for a Chromebook.
That's not true. Just empirically not true. Additionally, you didn't include fully-loaded costs in your blog. Trivially: how many hours go into testing and deploying updates? What is your AV update subscription annual cost? Those are just the first two I noticed without really re-thinking the problem.
Relating to software costs, have you heard of techsoup.org? They'll sell you software for cheap if you're a non-profit. For one of my non-profit clients, they sold them copies of Norton for $4/each. (I assume Symantec got to write off an in-kind donation, so its a win-win).
Just wanted to mention it, on the off chance its helpful.