BoA absolutely deserves some success in the U.S. I think she has all the tools to make it in the industry here, but is missing one thing in order to do so that I can't pinpoint.
Race & taste. BoA's US debut album was just like a downward version of Blackout, I mean look at the producers... Even Blackout wasn' successful in the States.
I was really rooting for Utada to make it . Her album did do pretty well compared to other East Asians who have tried to break into the market. I think it got up to #69 on the Top 200.
Mostly because lack of promotion. Also, the general music taste of the Americans is really narrow. Other cultures might have different kind of Music and it'll be hard to change their music style because it won't sound authentic and might end up just odd.
the American culture rules the world because America tops the list of the Globalization power. So it's much easier for an American successful singer to make it to other Countries. On the other hands, other countries in the World doesn't have the same Media power and Technological power that the US have, so It's much harder to make an impact and breakthrough.