The advantage of such a standard is obvious. The lack of a universal standard for numeric keypads is a problem. The user will type faster and make fewer errors if the keyboard layout is always the same. And blind people would certainly prefer that all telephones have the same key placements. The same applies to software user interfaces.
Consistency is important within a system as well as between systems.
A dialog box for saving files looks and works the same in almost all Windows programs. This regularity is obtained by defining the code for such a dialog box in the operating system rather than in the application program. This is a great advantage to the user because he can use a new program immediately without having to learn how to save a file, etc. Some programmers want to design their own dialog boxes in order to add fancy decoration. You should resist the temptation to do so for two reasons.