By definition, a perc is an addition added to bongs/rigs to cool the smoke down.
The whole point of ice catchers is for the ice cubes to cool the smoke down.
And regarding the comment about water... not all percs use water.
For example:
The freeze coil perc, which adds extra space with cooling gel around the chamber that cools down the glass for extended periods when refrigerated.
There are also tornado percs which make the smoke spin around like a tornado. Both of which exclude water from usage.
Not all bongs have ice catchers, which makes it an "added edition" by definiton.
I mean, it's possible to add ice to bongs without ice catcher percs... But they don't have the built-in glass to stop the ice from getting down into the base, or even breaking other percs below when dropping them down