I found this Washington Post Blog post dated 11-24-13, which tries to answer this question.

Quoting Michael Frank of the Washington Post:
“That price difference persists because it is extremely difficult to actually do the arbitrage, since Mt. Gox’s banking relationships in the U.S. were terminated by the Feds, so it’s difficult to get US dollars out of Gox and into the US. To do this you would probably have to shuttle the funds around through Japanese banks and/or by way of other intermediate currencies. This process is expensive (the banks will take a cut at each step) and so that’s why the price difference persists.”

Money and Legal issues abound
In 2013 the United States Federal government seized $5 million dollars from Mt. Gox and they are in the middle of $75 million lawsuit with a former partner. All of this has made it rather difficult for U.S. users to get their funds out of Mt. Gox. You can read more about MT Gox’s financial woes here. I highly recommend you read the entire article about Mt. Gox before you invest any of your U. S. dollars in that exchange.

A few excerpts from the Wired Article:
Mark Karpeles, the CEO of Mt. Gox gave an interview to Reuters in April 2103 sitting on a blue exercise ball, which did not spark a lot of confidence.

“The CEO of the most important business in bitcoin sitting on top of a bouncy ball talking about world-changing ideas, says Roger Ver, an early bitcoin investor who knows Karpeles well and considers him a friend.” You can see the Youtube video here.

“Prices on Mt. Gox are higher than they are on other exchanges — a reflection of the difficulties customers have withdrawing their funds.”

“Dan Held, the founder of bitcoin market data company, Zero Block, has less sympathy for Mt. Gox. He points out that the US government warned businesses like Mt. Gox that they’d need to register as money services businesses in March of this year. But Mt. Gox didn’t do this until months later — after the feds has seized its bank accounts.” “A lot of it, I think, is incompetence,” he says.

“They just think Mt. Gox is the biggest and the best, and they don’t know…”

I’d consider this a must read if your are thinking about investing your money at Mt Gox.

You can also read first hand from disgruntled MT. Gox users. This is a long forum thread from actual users.

Bottom Line, buyer beware!