remember that when the bucket shops tout the forex market as trading trillions each day, this is spread across hundreds of currency crosses. No individual retail forex broker comes close to the liquidity of the CME and Globex. When you have an account with a fx retailer, you trade its prices or not at all, subject additionally to the retailer's willingness to honor its prices -- and that is all the liquidity available to the customer. There isn't any more, as liquidity in other FX houses or ECN's is not transferrable. You are not trading in the spot market - you are trading against a bucket shop, so in reality there is no liquidity.
Globex has the third highest liquidity of ANY fx platform. Only EBS and Reuters FX beat it for liquidity. Remember that 1 Globex Euro futures contract is worth $125,000 notional currency, and with around 150,000+ contracts trading daily thats nearly $19BN trading on that one currency pair all in the same place, accessible by all - unlike EBS or Reuters.
Forex has a lot of $ business done for every currency cross in the world aggregate combining all transactions on all the disparate platforms and firms, but when you look at each pair individually at each firm, you start to understand that spot forex isnt as liquid as they want you to think.
If you put execution speed into the mix as well, globex will beat ANY fx platform including EBS - HANDS DOWN for execution speed. The OTC cash forex market is mostly used by traders or institutions who have genuine need to do business there for what ever reason, as in banks who need to deal in cash, spots or forwards as part of their business, but the markets that they access, such as EBS are generally closed to the majority of retail clients - hence why your average retail trader ends up dealing with bucket shops without really understanding the difference.
Futures also carry less risk than the OTC market - forex bucket shops are really the bottom of the pile - slow fills, massive counterparty risk (refco fx anyone), etc...
So you're absolutely right, hopefully FX Marketspace will be everything to everyone in spot.