Well, for starters it has to do with the Evo having that as an extra feature added to the system which I might add, only outputs certain video, not mirroring the entire display. What I believe most people here are concerned with is getting the composite out working (although I certainly wouldn't complain about HDMI) mainly because we KNOW it DOES work on both the gsm US and international galaxy s.
I understand it has to do with the system-on-chip for the gsm radio that includes this feature (for whatever reason its tied into the headphone jack and audio system), but the cdma system on chip doesn't. And I believe that's the issue. The fact that many phones that are designed as GSM and have awesome features just "thrown in" like composite video and fm radio, only to have those same features left out in the cdma variants. The FM radio too is part of this system-on-chip. And who is responsible for the system-on-chip? Good 'ole Qualcomm. This also raises another question. The Evo is an entirely Qualcomm system. CDMA radio, Qualcomm snapdragon CPU, and so maybe they decided to add the HDMI to make them look good, but intentionally left the analog video out feature off the Galaxy S in an effort to make the competitor look bad any way the can. The same way I believe Samsung refused to give screens to HTC for their recent smartphones (specifically Evo and Incredible, also Droid X) in an effort to try and take them on in the marketplace. The DIFFERENCE is Samsung (and thus we) paid for the technology (surely a high fee) only to have the bare minimum garbage Qualcomm was willing to supply. And although I have very little/no evidence to support it, I'm not entirely convinced Qualcomm hasn't had a hand in the recently discussed "150kbps upload cap" issue...(according to noobnl the RIL is a gsm to cdma wrapper rather than direct access:
cyanogen mod 6 port to the epic 4g - CyanogenMod Forum )