In TXL it is down to the experience and assessment of the situation of the tower controller on duty as far as i know. In general a take off clearance is given once the landing aircraft is well below minimum, usually around 100 to 50ft. And yes, in the past they would give the take off clearance earlier as well, which did lead to the unpleasant situation of one aircraft getting airborne while another went around leading to a very low separation (well, loss of separation to be honest), after which they changed procedures a bit. However, since then, traffic has picked up quite a bit which of course puts pressure on all concerned. And the orange bunch apparently quite often bangs on the door of the tower to tell them off for delaying one of their aircraft.