Disclaimer: I am not a CentOS user, so it is possible (but not likely) it does something strange... but...
From man bash:
Readline is customized by putting commands in an initialization file (the inputrc file). The name of
this file is taken from the value of the INPUTRC variable. If that variable is unset, the default is
~/.inputrc. When a program which uses the readline library starts up, the initialization file is read,
and the key bindings and variables are set.
So if INPUTRC is not set a program that uses readline will try to load ~/.inputrc by default. Does ~/.inputrc exist? If so, does it load /etc/inputrc?
Otherwise, setting INPUTRC in /etc/profile is a common way of doing that, but it could be anywhere, or nowhere, along the initialization chain (see man bash: INITIALIZATION for how that works).