Just to add some info on this topic. I have no idea how many cambelt changes i have done on these cars, rather a lot is probably an understatement. Anyway, i have yet to do a belt job or head rebuild simply because the belt has failed of it's own accord. They just don't break. The items which fail and cause the belt to break are all other components in the belt system. The water pump fails and siezes and the belt just burns through on it. The same goes for the tensioning pulley and the idler pulley. The hydraulic tensioner itself loses pressure and fails, which makes the belt go slack, it then jumps cams. These are all individual scenarios which is why it is always recommended to change the full system. I also renew the thermostat at the same time, why not, they can fail too so change it.
I realise that this is an old post but i thought i'd add the info whilst i'm here.