Question about the installation directory of programs

[ChenQi]

Hi all,

Forgive me if this is a dummy question.
I see the installation directories of programs are controlled by the 
applets.src.h file.
Some of them are installed into /usr while some of them are not.
Is there a criteria to determine whether a program goes into /usr or not.
For example, why is `rpm' installed into /bin while `tail' is installed 
into /usr/bin?

Best Regards,
Chen Qi