I actually agree with you here, in that at the end of the day, nobody owes the developer a living. I don't go around blowing money buying random apps I don't use as a form of "charity" for the developer; I buy apps because I feel they might be of use to me.
That said, I draw the line at pirating apps or otherwise finding a way to use a paid app for free, therefore depriving the developer of his much-deserved income. That's actually what I like about the iOS app store. You can't sideload apps or download them from 3rd party app stores (or at least, not easily). So the only way is to buy them the old-fashioned way. It's a win-win scenario. I get the app I want, developers get their cut, and are in turn incentivised to continue creating apps (especially higher-quality paid apps) because they know that people who want one will buy it the honest way.
Because the free app invariably pales in comparison to the paid version. I have students using open office because their laptops came without Office preinstalled, and let's just say that compatibility with our school-issued laptops can be a problem at times.
It's also more challenging to instruct an entire class on using the features of a particular software when different groups of pupils are using different variations of the software, each with its own quirks and differing takes on the same features.
As a teacher, part of my responsibility involves setting exam papers. How do you think it would reflect on me if I used pages or open office for the job, sent it to my boss who uses Office, and told her that the onus was on her to find a way to open the file without screwing up the content?
As is every other company out there. Welcome to the real world.