I know it's fun to hate on Apple but in this particular situation I actually believe they made the right choice going with Apple. Just to give my background, I'm an educator at university level but help manage the IT for a local high school so I appreciate the educational effects of the technology but also the management behind the scenes.
First off, students (and teachers) don't look after technology. Especially when it is not theirs personally (ie bought with their own cash). Our experience has shown the Apple products hold up much better to abuse over time than the $150 Android tablets you mention. There is also a larger (and in our opinion, better) selection of rugged cases available to further protect them. After a few years of abuse the iPad is still working (though covered in scratches), the Androids are largely broken messes.
Apple devices also have a good history of recieving OS updates. Sure they slow down over time but you don't have to apply the updates if you don't want. We find that applying updates for the first 2 years after purchase is beneficial but after that we test before deciding to update or not. With Android you have no idea how long (if at all) the vendor will support with updates.
So from a monetary point of view the total cost of owership (and experience) is actually better (for us in our opinion and situation) over many abused devices over a 3 year lifespan. We are keeping an eye on things though and Android/ Android vendors are definitely improving and closing the gap. If our opinion changes down the track we'll happily switch over.
In terms of software/ apps. Couldn't care less which has the largest app store etc. Only care which has the most useful apps/ software for our purposes and again Apple wins here (in our opinion).
In terms of educational value, again I believe this is a big picture, long term proposition. Like any technology, the value is not in it itself, it's in how it's used. And like any other technology, it's going to take a while for our understanding of it's best use to evolve and mature. Of course it's not going to have immediate and obvious benefits straight away but you have to go through this learning stage to get there. You can't just magically jump straight to the benefits stage. The normal teachers are just using them as glorified text books right now but they are also getting used to them and how they work and how to manage a class with them. The innovative teachers (and students) are experimenting and learning and doing fantastic things with them. Over time that will filter down to the rest.
Also, I hate it when people judge the value of something based on if it improves exam marks of not. Exam marks are worth didly squat once you get out into the real world and we're focusing way too much on them as opposed to the the skills you really need out in the real world. Technology, applied thoughtfully, can help students develop many skills such as problem solving and creativity and team work and understanding how and why to be socially responsible etc and these are skills which are hard to measure and we largely ignore as a result.