Google killed the hardware menu button with the Galaxy Nexus and Android 4.0 Ice Cream Sandwich. However, OEMs like Samsung and LG have been reluctant in killing the button and till this day provide a hardware menu key on their devices, instead of the much more useful multitasking key.
However, that might change since Google has hit the final nail in the coffin to kill the hardware menu key with the Android 4.4 KitKat update. Post the KitKat update, the on-screen overflow menu button that replicates the function of the hardware menu key will be present on every device, irrespective of the fact whether it has a menu button or not.
Below is the comment on the commit from the author of the code, Adam Powell -:
This means that Galaxy S4 owners should be seeing the overflow menu button in all apps, even though the device already has a hardware menu button. Since this change has been committed in core Android, Samsung or any other OEM cannot change this functionality.
It will be interesting to see if Samsung and other OEMs will map the menu key to function as the multitasking button or still let it act as a menu button. The menu button has always been a headache for users that keep jumping from one Android device to another, and developers who have to make sure the overflow menu shows up properly on these devices.
While this change might not be appreciated by some lovers of the menu button, it will ultimately benefit the developers and end users in improving the usability of Android OS across the various devices.