Google has decoupled another app from Android in a bid to make it more accessible and easier to update. This latest app is Google Text-to-Speech which is used not only by Android itself but also other apps to read aloud text displayed on the screen. For example, it is used by Google Books to read books aloud and by Google Translate to let you hear how a word is pronounced.
As with other apps that are now available through Google Play rather than in Android, Google will now be able to update them without needing the support of carriers to push out updates.
If your device does not have this app or offers an alternative that does not meet your needs, it will now be easy to install and enable (Settings > Language & Input > Text-to-speech output. Select Google Text-to-speech Engine).
Google Text-to-Speech app is now available for devices running Android 4.0.3 or higher.