Well, I think Illaparatzo-sama answered these questions quite nicely... but I figured I'd add a little info of my own.
Newgi said:
Why Hyde of LArc-en-Ciel and Gackt of Gackt Job never did a WORLD tour together or for that fact with any other JPop/JRock band?
Well, if you're going to count JPop through history, then there have been at least a couple of groups which mounted world tours... didn't Yellow Magic Orchestra have at least a couple in their day (late '70s / early '80s)?
And did they necessarily have to be the opening act? I know Sadistic Mika Band opened for Roxy Music on a European tour... and of course Shonen Knife opened for Nirvana on a tour, though I don't know if that was a world tour or simply a U.S. tour.
And of course, if you go WAY back, I'm certain Kyu Sakamoto did some world touring in support of his international #1 hit "Ue o muite aruko" between 1961 and 1963...
The other thing you're forgetting is this... plenty of JPop groups have tried (and failed) in the past to break onto the international (or simply U.S.) music market. Pink Lady tried it in the early '80s, Seiko Matsuda tried it in the late '80s, Hikaru Utada has tried it twice now... and the only one with any *real* success to show for it is still Kyu Sakamoto from 1963 (only Japanese artist to reach #1 on U.S. Billboard charts). And all of the previously mentioned artists would be considered by many to the the *most* popular or successful artist of their particular time period... so what message does that send to the rest of the pack of JPop groups? If the best can't make it...
So certainly JPop/JRock groups will flirt with the U.S. audience, but how many do you think are *actually* interested in trying to become BIG American groups? Utada is certainly trying, but she essentially grew up as much in the U.S. as she did in Japan... other acts like TM Revolution and L'arc~en~ciel may view their one or two U.S. concerts as simply a feather in their cap as artists... they can revive/strengthen their fanbase at home by showing that brief moment when they played to a crazed concert hall in Baltimore. TMRev definitely capitalized, finally scoring his third Oricon #1 hit with "Ignited" after his Gundam SEED work as well as his heightened exposure in Japan thanks to a successful U.S. visit...
I'm fine with my favorite Japanese artists staying Japanese, honestly... part of why I like them is because they're Japanese artists speaking from a different point of origin than myself. I have had little difficulty getting any J-CDs I could possibly want thanks to the Internet... and if these artists ended up changing themselves in some way in order to please a mass U.S. market, I would end up not liking them as much (UTADA's "Exodus" is a great example of this for me).
So just enjoy the music however you can, be it from a Tofu Records CD sitting at your local Borders *or* from an imported CD that ended up taking six weeks to arrive... none of that should change your enjoyment!