I like Oanda, but you've got to remember that a broker != an exchange.
A broker has a price-feed which they take from an exchange - they act as a middle-man between you and the exchange they post your trades on, which has limited value when you can trade directly with the exchange yourself.
That is correct but for retail customers who trade Forex on Oanda, it isn't like you can go to a forex exchange to trade more directly. ie: ETrade is a middle man between you and the NYSE, but you can't go to the NYSE directly to bypass the broker.
In the case of something like BTC there's no centralized single exchange they'd be front us, so they would need to match buy/sell orders and act as their own exchange, basically.