I believe they disabled the text-to-speech on the Kindle is because it basically makes it easier for people to pirate e-books. The way it would work is that text-to-speech engines on a e-book basis can be translated via a speech-to-text software.

If you have something consistently pronouncing words in a perfect manner (text-to-speech, eg. the Kindle's text-to-speech feature), there is nothing stopping you from downloading the latest voice recognition software (speech-to-text, eg. Dragon Naturally Speaking) and having it scribe the entire e-book you paid for onto a MS Word document or PDF. From there you upload that to your local file host and POOF! no more DRM.

I understand what you are saying about other features possibly being disabled, much like how they had those 1-time use rental DVDs back in the day, but I think the text-to-speech is a feature that definitely needs a killswitch due to its potential usage.