I'm not sure about the "ethics" of non-constructive criticism from a developer perspective, but I think it is completely justified from the customer perspective. I paid (a lot) for this phone, I am allowed to be unhappy with the direction it's going: 1. As a market signal to the creators (which serves as very useful feedback), and 2. Because realistically I have to upgrade or be forced to not get any updates for my apps either (just in case someone wants to chime in that I "could" stay on iOS 6).

That's kind of the interesting thing we're seeing here that doesn't fit your analogy: most of the people complaining this time around are the iOS people about iOS.