It was a long due! With Honeycomb, and then Ice Cream Sandwich, Google took the initial steps to kill the Menu button on Android. Today, in a blog post on the official Android Developers blog, Google has taken the final steps neccassary in killing the Menu button.
The Menu button will be replaced by the Action Bar and Action overflow in the all the Android apps from now on. Considering no future Android phones will be coming with a Menu button, this was a much-needed move, as it will help in delivering a consistent UI across the Android OS and apps combined. Google has also strongly recommended developers not to use an on-screen ‘Menu’ button on their app as well.
The blog post at the official Android Developers blog clearly mentions all the steps which the app developers need to take to use the Action bar on their apps, and to maintain compatibility with older versions of Android as well. The Action bar in an app should incorporate all the important functions a user needs access to, and if the action bar is not sufficient, then they can use the Action overflow option.
Readers and Android app developers can find more information over at the official Android Developers blog.