Originally Posted by Prime
Because Jedi don't say, "What up, dog." Duh!
If it was him though, you'd think that Qui Gon would be like "Ah ha! Another Jedi Knight! Excellent, we're in a bit of a jam here see, can you lend us some money or a ride on your ship so we can get out of here? Or perhaps you can send a message to the Jedi Council for us as this is quite an urgent matter and we're stuck on this backwater planet, etc"
Isn't the EU explanation that at this point Vos has amnesia and doesn't know he's a Jedi or something like that? Still, you'd think Qui Gon or Obi-Wan would sense another Jedi nearby... maybe not. It would seem unusual for a Jedi to be just hanging out on some backwater planet outside the Republic, wouldn't it?
You could also say that ROTS doesn't make it explicit that it's Quinlan Vos, the EU character. Obi-Wan just says "Master Vos" (and it's not like two people in the Star Wars galaxy can't have the same last name, even if there are only 10,000 Jedi). From what I hear, the novel or comic of the movie makes it clear Quinlan is meant and that he gets physically torn apart by an explosion, so it was intended that he died. In any case, a peripheral character almost-cameo of a background extra expanded into an EU character, then mentioned in passing in a G-level source. I could care less about the character, but an interesting situation nonetheless.
If you view this as an Easter Egg (retroactively speaking) then you can just ignore it (like the shoe in the asteroid field or the TIE Fighters chasing an X-Wing on Coruscant). Or you can try a retcon explanation as to why this Jedi is sitting there and doesn't lift a finger to try to help his comrades or even acknowledge them (and vice versa).