I think you might find the reason is a little more mundane for BA. The policy of 'push and hold' is due to lack of stands. Sometimes we are allowed to wait on gate but most of the time the stand is needed. Try spending a day with the department that deals with stand allocation and you will learn the extent of the problem. T4 early morning is a nightmare.
The problem will soon be resolved though when we get T5 in 2007.