this question always comes up now and again! Unfortuantley not - they reason being (given to me by a senior dev at one of the larger outfits a few months ago) is that while there may be an incentive for them in terms of increased volume of trades (hence spreads being paid) there is a huge risk they get totally done over by any automated system since their is an issue of the "quality" of their prices on certain instruments
What you are seeing instead and will continue to see is increase in the functionality they offer e.g contingent orders which CS just introduced and IG have already had for a few months.
However a Market Data API might be nice and not present the risk I mentioned above I beleive