The problem is that since oanda charge for the *use* of the API you will simply never get the kind of following that IB has or applications like brackettrader because you would pay for using it as well pay to buy it.
If oanda want to charge for using the api fine but they could get smarter on charging for 3rd party addons and maybe take a cut of the sale price. That way things like brackettrader would make their way over to oanda and you would be charged for buying it or even a smaller monthly charge.