1. Don't mess with the oringal title or the fans will castrate you
2. Don't mess with the oringal title or the creators will castrate you
3. The name is awesome
I dunno. Gatchaman is a pretty weird situation in that I think there was more than one western adaptation (G-Force and Battle of the Planets?). I could be wrong, but the western versions were changed significantly (the ninja/espionage aspect reduced for instance).
I guess they call it Gatchaman because it will be pulled from and follow the original Japanese show.
It's kind of like how Macross and Robotech are two entirely different beasts, even though one was used to make the other.
In Japanese, "Gatchaman" has no meaning--it's onomatopoeia, a "sound word" used to give the feeling of the sound of big, heavy mechs slamming together in battle: "GATCHAAAN!" The show's creators had little knowledge of English at the time, and didn't realize that it sounded a lot like "Gotcha, man." Maybe they would have changed it...
Gatchaman is the official name of the leader of the group (Ken), and is only used to describe the group of ninja when all five are together. When they are separate, the other members of the team are referred to as the Kagaku Ninjatai (the "science ninjas"). They aren't called "Gatchamen."
The pre-production name for the show was "Birdman," which was changed at the last minute and is still written on the canister holding the film to the pilot episode.
It's no worse than a Go-onger, or Sun Vulcan or any other number of Japanese shows.
I know what you're saying though, Keith. I can see the general public not really getting it. Worse, there are people that will look at it and go "Hey, I remember watching G-For ... Huh!?! Why is it called Gatchaman now? What is this?"