Lets not be naive guys, lets see reality for a bit: iPhone 3rd-party repair market is ridiculously huge and Apple wants to harness that revenue. Heck, I've repaired my own stuff more than once, ordered a dock connector/speaker on eBay, went on ifixit.com, and changed the part. We humans like to repair stuff and not all of us are rich to have 'official car dealer' always repair with brand-new parts.
Worse case scenario, why should Apple brick a phone when they could just disable the touch-id function? There is just no reason other than greed, because when Apple bricks your phone you have no choice but to either buy a new one or bring back the bricked phone for repair. Which means more profits for Apple.