From an interview with George Takei.
These are Takei's words:
"[J.J. Abrams] asked me if I'd have breakfast with him. He told me he'd been interviewing many actors for the part. He tried as hard as he could to find an actor of Japanese ancestry, which is what I am, but he found another actor who he thought would be wonderful. So he wanted to get my reaction to that.
I asked Gene [Roddenberry] how he came up with the name of Sulu. He said he wanted the Starship Enterprise to be a metaphor for Earth. So he wanted the people to represent regions of this planet. So Uhura was African and her name was based on a Swahili word.
So he was looking for an Asian name for what would be my character. Now Asian names are very nationality specific; Tanaka is Japanese, Wong is Chinese, Kim is Korean. Now Asia also has a reputation for warfare and colonization. Roddenberry didn't want to bring that into that character. So he was looking at a map of Asia and trying to solve that dilemma. He saw there was a sea called the Sulu. It's in the South China Sea area. He thought, ‘the waters of the sea touch all shores.' So that's how he came up with the name Sulu.
So I told this story to JJ. I said it would be entirely in keeping with Gene Roddenberry's vision. I told him not to confine himself to one particular cultural group. If he felt that actor could bring that kind of talent, he should go for it. So, assured by that, he told me he was looking at John Cho."
Takei's story makes sense, and the comment he makes toward the end of that quote, "I told him not to confine himself to one particular cultural group. If he felt that actor could bring that kind of talent, he should go for it.", is exactly how things should be.
But i would point out that John Cho would never have been cast as Kirk (even though i'm sure there are people with Korean ancestry in Iowa in the 23rd century); so it seems that, rather than being an expression of an unprecedented-ly egalitarian attitude towards acting, it's more likely that there's this idea that it's okay to fudge the race of a non-Westerner (hell, historically, it's been okay to fudge the race of a Westerner who looks a little bit brown (i.e. using South Italians to portray American Indians)).
And i would highlight this line;
He told me he'd been interviewing many actors for the part. He tried as hard as he could to find an actor of Japanese ancestry, which is what I am, but he found another actor who he thought would be wonderful.
Still find that hard to believe. John Cho has a lot of pop-culture cred at the moment. Star Trek was billed as aiming for a pop-culture-y audience of 15-25 year olds. I just find it difficult to beleive, firstly, that it was SO DIFFICULT to find talented Japanese actors going for the role of Sulu (they must have been flooded with people of Japanese, Scottish, African heritages as soon as the movie was announced!), and secondly, that this had nothing to do with John Cho's status, popularity, fame relative to any Japanese actor you could name (excepting women, and men who would be too old for the part).
Which is not to discount Takei's comments, or his interpretation of the character's significance as someone who was literally always intended to be "specifically Asian, but not specifically Japanese", to paraphrase my earlier post. There you go.
That ought to be the way Cho's Korean-ness relative to Takei's Japanese-ness, if it is an issue at all, is seen. I like it. It's completely in keeping with Roddenberryism.
But you still maybe get a story about the way actors are chosen in Hollywood, and the way less well-known actors could be locked out; it's just that race happens to be the factor that highlights it. Having said that, i've never heard of Zachary Quinto or Christopher Pine before.
Edited to add:
This is beside the point (or IS IT?), but look at this line: "[Leonard Nimoy and Zachary Quinto] are both talented actors. Their personalities are alike, too. You know, Leonard and I used to talk a lot about political events. I'm a political activist, and so is he. We used to talk about the headlines all the time." Need time machine and tape recorder. Oh, i have a tape recorder (from mistersteve)! Halfway there.