I don't think that you should have to protect your device from normal use.
Other than the wake & volume buttons, there's only one button on the phone in normal usage - you'd expect it to last, unless 'abused'. Maybe we're just "pushing it wrong".
I did have a 2nd hand iPhone 4 before, and after a few months the Home button started failing sporadically. After having it fixed, I got a lecture from the shop staff on how I only need to tap it, not push it in.
I used the Assistive Touch button for a while when it wasn't working, but it got in the way far too much for me.