As someone who runs the IT for schools, allow me to jump in.
All these manufacturers are NOT chosen by the IT department of the schools. We suddenly get some login details emailled and a guy on the phone asking for our entire school database, and that's the first we hear of anything. The maths department would be generally to blame for Mathletics, for instance.
Then we argue and fight and point out the holes and get made to do it anyway. We do this, in a way compatible with Data Protection (yes, I've told staff where to go AFTER they've paid for products because the data would be hosted in the Cayman Islands and things like that and I refuse to do that as it's a breach of the DPA and similar EU rules), and get the service running.
It's then pushed "because we spent a lot of money" and - primarily - "because other schools do it". The parents complain. The IT department fends them off for several months (we know it doesn't work, there's nothing we can do - yes we'll "pass it on" to our suppliers - guess what the answer has been for Mathletics for the past two years? "We're working on non-Flash versions". TWO YEARS). Then eventually, people get bored, ignore it, carry on. Whether those people are the parents, the maths department or the suppliers, the system dies a death.
Would you like me to tell you how many similar things I have in my network and on my list of services at the moment? I'm actually HOSTING an internal resource that isn't iPad-compatible. In a school full of 1:1 iPads. It was purchased, so that means it sticks around until the person who got it authorised leaves, and about 1% of the games on it are actually iPad (or even touchboard) compatible. There are promises, as always, but little momentum.
Even things like Apple Pages vs Office - people just assume all computers are the same and that they all work identically. Even with management - powerful MDM does not provide anywhere near the same level of control over an iPad as GPO does over a PC. Or similarly for Macs. And "Why can't our Macs run *insert some ancient piece of software written for Windows 95*.
Good schools listen more, but never listen completely. And because it's someone's pet project, they push it through, ride through the storm, and then claim success - and then a couple of year's later use that success to get a job elsewhere and everyone still complains so we just scrap the "old" system and buy another almost identical in its range of problems. And, yes, parents do sometimes think that having some computers in the IT Suite is an acceptable solution. But mostly not.
IT in schools is immature and the purchasing decisions are not made properly. Even where IT specifically point out incompatibilities and problems, sometimes they are rode over because "other schools do this". And then when you speak to their IT guy you find he had the same argument pulled on him and we're all just following some idiot somewhere who didn't think through their purchase in order to be the same as everyone else.
That said, there is an amazing lack of cross-platform compatibility in educational software. As this proves, even being "web-based" doesn't save you the hassle of it not working on Chromebooks, Macs, iPads, Android, their mum's phone, or whatever. The magic word at the moment is "HTML5", but even there I've seen things that render atrociously on small screen devices because just being HTML5 doesn't mean that it actually was thought about. And then you get into "How do I filter videos, games, etc. that are written in HTML5?" - because that's much harder than it sounds.
Hell, it's common practice for my suppliers to tell me to "just unblock" the entirety of the Amazon Elastic Cloud so that their cheap servers aren't caught up in our filters. And they are serious. And there's little I can do about it if we want that expensive new service to work.
It's the school's fault, yes. But also the manufacturer's. And, in a way, the people who encourage iPad (not "tablet", notice, but a specific, branded, particular tablet) use in education.
400+ iPads and counting...