Incidentally, why do you think this is 'infancy'?
Personally, as someone who has managed an E-Commerce book I couldn't disagree with you more. I'm not trying to paint the SB firms as whiter than white here, but there is a very key point that that policy makes, and it's one that the retail community just doesn't seem to grasp.
Liquidity in broad terms in the FX world is huge, but that isn't at all the same as saying liquidity at any given instant at any price point in any currency pair is infinite. So if as a market maker I am asked to quote a two way price in say EUR 25m, the spread won't be the same as if it was EUR 100m (as the cost of my exiting the position will almost certainly be greater). Thus if a retail trader is being streamed a continual 2 point price in EUR/USD, that 2 point spread isn't good for an infinite amount of Euros, as there aren't an infinite amount of Euros available to the SB firm to get out of that position.
In interbank / wholesale circles if I hit a bank's price and it isn't my full amount (i.e. if 2 seconds later they get another call from me asking for a price in the same amount, or if, as some hedge funds do, I conduct what's called a 'drive by' and call like 10 banks at once in $30m rather than one bank in $300m), I would expect angry phone calls.
This is what a lot of the retail community don't seem to understand - much of the wording there is protection for the SB firm against the prospect of some mass co-ordinated action whereby 100 clients get together in some chatroom and say we're gonna spank EUR/JPY today at precisely 3pm or whatever. Then they all hit their respective platform in small size repeatedly, leaving the SB firm(s) caught long and wrong with no way of getting out of their position at anywhere near the rate they got in.
You can't have your cake and eat it guys - any price is always good for a certain size. It's not a conspiracy, it's just the facts of life.
GJ