becuase of the EEID. swap EEPROMs and itll work fine. You have to remember Apple has always been up to their dirty old tricks since day 1 of the operation. (proprietary, closed system, etc..) kinda like IBM was.
usually, some, if not all, have EEPROMS that tell the video BIOS/GPU what the panel model/type is, the max resolution, etc. known as the EEID. there is a dedicated EEID bus. some machines use it, some do not. The purpose for a machine to use an EEID is if the motherboard is used in several different display configurations. If the EEID is not used, usually its becuase of the motherboard only working with 1 screen type or resolution.
Apple is the same way, but they DO use the EEID. But, against us. the EEID reads back LM171W02(TT) (for a g5 isight), the mac will boot. anything else, the mac will not.
This goes for most if not all of them. You can swap out the eeproms that contain the EEID, and it will work fine. the system will see a TT panel even though your using a TL. vice-versa.
you can use 3rd-party panels the same way, as long as the resolution matches, etc.