1) Why should there be a bunch of japanese actors/actresses in Hollywood? Last time I checked Caucasians weren't really well represented in the HK or Bollywood movie industry. I mean, just think about it for a bit - pretty much every region of the world has its own entertainment industry, the only reason why the USA's is so ... hmm I guess "important" or whatever, is just because its the one that makes the most money and is seen by the most people outside of its native region. Because of this is often alot easier for people to get involved with their own native entertainment industries. As you noted there are very few foreign born actors in Hollywood and infact I wouldn't even consider Jackie Chan or Jet Li to be "Hollywood" at all, I doubt they would either despite being in a few Hollywood films. And why would they care? The HK movie scene is pretty rad and they have more than enough wealth and fame in Asia that the fact that they have popular American recognition is just icing on the cake.
Basically I guess what I am saying is that American movies are made for a domestic audience first and foremost. Because of that they are more likely to star American actors/actresses regardless of ethnicity. Obviously the rule bends a little bit when it comes to English and Canadian actors as well, but for them the draw of comming to the states to perform is pretty damn high - there is no language barrier and we can all pretty much fake each others accents, Eh? The only reason why anyone outside of the States sees these things is because there is money to be had exporting it.
Lastly - I'm not so sure that most Japanese actually
care enough to actually want to work in the states given the logistical work involved when they have their own perfectly fine movie industry. I mean, as much as I love HK action cinema, I'm not sure that my first choice would be to fly over there to try and work in movies (if I was an actor anyway) - especially given my total inability to pronounce most chinese words correctly. (I swear I spent 10 minutes being coached by my girlfriend and her brother and sister on how to say something and they kept saying, "no no, its like
this" and I was going "But thats what I said!!! *slams head into table*"
2) English skills don't matter to much if you're acting, you just memorize lines and repeat them. This is why when I'm driving with my girlfriend I can understand HK pop if they sing in English, regardless of the fact the singer in question doesn't actually speak it that well.
3) Funny you should bring that up, in the States a measure of someones "American-ness" can be directly related to how well they can affect an American accent. Obviously since we live in an extremely heterogenous society the only way that we can identify each other as Americans is by our language skills. Completely the opposite of Japan where if you basically don't look Japanese you are pretty much always gaijin regardless of if you hold citizenship or not or if you can affect fluent Japanese language skills.
As far as tolerance towards accents go... this is basically very dependant on how much exposure someone has had to different accents. I don't think it makes anyone feel wierd but it definately can make it hard to understand people. For instance I used to have a really hard time with a co-workers really pronounced Indian accent, but after a few months I got to the point where I could understand him (Although I hate how he shakes his head left-right instead of up-down when you are explaining something, I'm always going: Sri! Up down is yes, left right is no!! You're making me confused

" Also I got a pretty good handle on understanding accented Chinese as well - although my GF and her siblings are all Americans, her parents are immigrants so when we first started going out I had a hard time understanding her folks. Her dad was pretty good because he used to lecture at college, but her mom has a very classic sloppy southern Chinese slur and it took me forever to understand what she was saying.
Oddly enough I have the least problems understanding Japanese accents unless they are REALLY bad. Infact most Japanese I have worked with here in the states get a pretty good handle on pronunciation within a few years and infact one of the best non native english speakers I have heard was my friends wifes father (what a mouthful). He is a naturalized Japanese-American (by marriage) and he actually has a bit of a midwestern accent.
Oh and in a slightly related topic to accents - one of the most humorous moments I had was when my GF's cousins came up to visit for her brothers wedding. They are all from Atlanta, Georgia. For some reason I found it hysterical to see a bunch of Chinese people talking with outrageous southern drawls. I think it was the cognative dissonance between two pretty bad stereotypes - The smart Asian guy and the stupid Redneck.
Funny stuff.