Readline current reads its configuration from /etc/inputrc. That is fine, but it should also include any configuration from ~/.inputrc. That way you can have system-wide config in one file, and user-specific in another. To do this, just add this to the end of the default /etc/inputrc:

# Read user-specific config
$include ~/.inputrc

That will save a lot of frustration of people wondering why there readline configuration isn't working...