Estimating price sensitivity and working out the right price for both your core product and value added services is traditionally tricky in the airline business because of capacity control. Normally when you put the prices down demand increases but in an airline revenue management environment you put the prices down because you are expecting lower demand. Accordingly it is difficult to isolate the 'normal' effect.

Add to that the fact that BA has never done this kind of unbundling before and that they will have had no data on the demand for this service on their planes. Then I would have been surprised if the price had not changed because that would have shown that their first guess was perfect.