Ok, I never actually looked at the law, or the opinion. I just took the interpretation I heard from my friend as the truth. I just looked up the actual law (O.C.G.A. § 40-6-120(a)(2)) and read the Georgia Supreme court opinion (PDF). It looks like you are right and it just made the law about the lane to turn into unconstitutional.
Now, IANAL, so don’t take any of what I say about laws as the truth or not.
Maybe they’re from places where it’s directly I-llegal to go anywhere with a red light and have been told its legal to turn right on reds but didn’t understand it correctly.
Maybe they’re from places where red lights are treated like stop signs.
Maybe they’ve had a brainfart.
Maybe they’re morons.
Take your pick…
Twenty quatloos on the “moron”! 
Same reason they run red lights in any direction. Even right on red is only legal when it is clear to do so even though some states do not even require you to stop at them.
Meeko: You should come over here. South Korea has a “right on red” provision in the Road Traffic Law; however, almost nobody actually stops–or even slows down–prior to the right turn.