Why do heavy departures wait 5-10 minutes on the runway at ZRH? I'm frequently travelling to Zürich for business and I usually make my schedule so that I have at least an hour to do some planespotting and photographing at the ZRH airport.

Whenever I came to the airport, the runway usage was the same: RWY14 for all the landings, RWY28 for almost all the takeoffs, while RWY16 was used by heavies for takeoffs (usually the flights to Asia or to the USA). I noticed that once a heavy aircraft lines up at RWY16, it waits for some 5-10 minutes before it starts rolling (although it is already way behind its scheduled departure time). The only possible explanation that I could think of was that its engines would cause severe turbulence for the airplanes which are landing at RWY14 and that it has to wait for a significant gap between the landings.

Am I right? Or if not, does anyone know the real reason for these delays?
The usual reason is, that departures from runway 16 are not allowed to climb straight ahead due to noise restrictions over downtown Zurich. Instead they need to turn left, where they cross the departure path of runway 14. So if there are arrivals on 14, no departures on 16 are cleared, as in the case of a go around on runway 14, its departure sector must remain free. I've been watching planes stuck for half an hour at the line up 16 for that reason. Imagine that waste of fuel... ZRH's runway capacity, despite having 3 runways, is thus actually lower than for a parallel 2-runway setup (think about London Heathrow e.g.).