As far as I'm aware most bitcoin exchanges don't adopt fiat currency as it requires them to be licenced with the money markets.
The same goes for the forex markets which exist such as IG Index or Capital Markets. The situation which would allow them to trade bitcoins for money is not suitable as it's not recognised as legal tender and organisations such as the IMF would not accept trading on licenced exchanges.
It's rather safe to assume for major players in the money markets would be unable to adopt bitcoins due to the red tape involved.
A small quote from the best exchange I am on
"Financial Regulation
Our business and services are buying, selling and trading virtual goods and commodities. We are not currently regulated as a financial institution."
I would imagine that a real problem is that the bitcoin market is just not large enough for most forex traders to care. If there are around 8 Million BTC out there with BTC in the $4-5 range the total value is to small for people who are used to taking out Million dollar positions – Zachary K – 2012-02-21T09:25:10.843
2You'd be surprised how quickly people can learn new stuff if there is serious money to be made after doing so – Gary Rowe – 2012-05-22T09:09:53.390