This is an interesting debate. Coming from Australia - I have NEVER seen a builder plaster over plasterboard. My understanding is that plasterboard was invented to avoid this unnecessary process! Same applies in the USA. Plasterboard has been used in this way (without a skim) for at least 30 years that I know of in these other countries due to nearly every house being timber frame but because its uptake here in the UK has been more gradual I suspect that wet plasterers are simply clinging to their trade.
I really don't believe the finish is any better either. In fact my experience with trying to put fixings into stud walls that have had a skim coat is that the skim readily cracks immediately around the fixing point. Also, a slight knock also promotes cracking and chipping which you wouldn't otherwise get.
To quote an Oz builder friend of mine - "why would you buy all that extra material, waste all that water, spend all that time mixing and applying a finish that isn't even necessary and run the risk of cracking."
It seems to just be a UK practice or is every builder in the US and Australia wrong?
PLasterboard was invented as a replacement for lathing plaster, not to avoid plastering.
Timber framed building was not deemed suitable for UK climate until relatively recently, whereas it suited Oz quite well.
To be fair to you, if you haven't been looking at skimmed walls vs joiinted walls, you probably don't have the eye to tell the difference but it is quite noticable. How can you hide a butt joint on a board, especially on a ceiling when you have to put 3mm on the join and nothing on the middle of the board? If you don't have the eye to spot 3mm ridges on a ceiling, then quality of finish is hardly likely to concern you!
Jointing in winter and wet weather here is very time consuming, often taking several days, a week even, for it to take a sanding down. Once the temperature is above freezing, a skim coat will be finished within hours, regardless.
The oposite is true, in that it is harder to skim in warmer weather such as Aussie summers have, so jointing is easier.
The problems with fixings I just don't get, I'm afraid.
The 'chipping and knocking ' I don't understand either. It is better to chip the skim than break the paper of the board.
As for running the 'risk of cracking', it is not the finish that causes cracks, it is the boards underneath that move. The tape that covers the joints is usually the same if you tape or skim.
The main reason in the UK for jointing rather than skimming is that is is cheaper to do , and easier to find the people to do it as it is less skilled work.
Finally , as for clinging on to the trade, in the marketplace, the client dictates the finish, not the other way around. Traditionally, the UK builder /housebuyer prefers the superior finish of skimming. The move to boarding and jointing here is down primarily to cost and also to the shortage of skilled labour
I know of NO builder who would not skim his boards if he could get it done as cheaply as tape and joint - ask a few of them and see if this is not so.