yes, SQ and CX sometimes dont serve it on the ground, even in USA, due to custom regulations. but in that case, they should just buy some duty-paid champaign for the service on the tarmac, like other airlines do. it is just a cust cutting measure.

for RUH, serving on the tarmac even after doors closed is very very dangerous. i only from out private jet ops that it makes sense to leave saudi airspace. in saudi airspace, alcohol is simply not allowed and alcohol containers need to be sealed. if you take off, have a problem and need to return to the airport without leaving saudi airspace and all seals are broken, you will really get into trouble.