Air Berlin do now offer through ticketing, but i don't know the terms and conditions etc..
I just don't get the philosophy at BA, running down a quality product, as that feeds their long haul network, both on departure from the UK and upon arrival. I try to avoid BA connect when there is an alternative with a proper airline. Heck, klm can still do freee food and drinks (including alcoholic drinks), and at lower prices than BA or BMI.
If a travelinn/lodge/budget hotel opens up in the same street as a five star, the five star hotel management do not immediately decide to become a budget hotel. Instead, what savvy management does is use every trick in the book to differentiate itself from the budget chain, in order to justify the fact that it may be more expensive.
I personally think BA have lost the plot, and will probably end up like BMI domestic, who no longer seem able to offer through ticketing, unless travelling business class (which on BMI is exactly the same as economy but costs more). I guess that's what you get with a budget airline minded man in charge. BA should be thinking nothing but quality - it is what they are good at, just as ryanair or easyjet are really good at the budget approach.