It has nothing to do with Linux because Linux is no one thing (at least, not in common parlance.) Text to speech is different from speech to text (voice recognition.) TTS has been a solved problem for a while, and there are numerous solutions in Linux. Speech to text is much more difficult and requires more specialized knowledge that doesn't have much presence or interest in the various open source communities. Heck there's a whole article on it at Wikipedia: http://en.wikipedia.org/wiki/Speech_...ition_in_Linux