The BlueTooth module is added as a discreet module to the Power Mac G5s, I believe. On the iMac G5 it is actually a part of the motherboard itself, there is nothing to "add" or "remove."
When you get an iMac G5 with BlueTooth and wireless keyboard/mouse, at least, you only get the wireless keyboard and mouse and a setup assistant pairs the devices when you first turn on the computer.
This may be the future direction for this feature as more and more BlueTooth devices are available (including Apple's own wireless keyboards and mice).
Of course with pro Macs the tether to wired devices may linger for many more years to come.