Let's be realistic here.
To successively cross-over into the Anglophone market, one must be fluent in English.
There are very, very few popular singers in the Anglophone market that are non-native English speakers. Shakira is a rarity.

Another thing is that we have to consider what "making big" actually means. As fans of Asian music, are views on the popularity of these artists are very skewed. Rain, Seven, Wonder Girls, even Utada, these artists are not known to the average public. They have no idea who these people are. Even someone who saw Ninja Assassin has no idea who Rain is.
I think FEM and Charice are fairly well-known. As much as I dislike their song, "Like a G6" is very popular right now, and they even appeared on a talk show (Letterman?).
Charice is getting recognition for her guest spot on a really popular TV drama, Glee.

I'm not really sure if it's impossible to become successful as an Asian, as if their is some inherent racism. Many Anglophone artists are actually well-aware of the Asian market, such as Lady GaGa, Kanye West, Ne-Yo, and others.

If Utada or somebody else could "feature" on a really popular artists song (Like a Ne-Yo + Utada collab.), then I think that would boost their popularity.

(Personally though, I don't like FEM, Rain, Seven, Wonder Girls, Arashi, KAT-TUN, Ayumi, or Kumi, nor do I want them to debut here, successfully or not.)