Uk health care costs a fraction of the cost that health care in the US (Can include any other country in Western Europe as well as Canada and Australia). Medicare IS actually somewhat like Australia, I believe. It is a single payer but not provider. Though I don't know which systems are single payer or single payer/provider. NHS is the latter. However or medicare it is only for people over 65, as well as disabled people.
One reason to cut costs is for "cosmetic surgery", I don't agree but this is where top surgery is. And insurance doesn't normally cover. So a good reason to cut costs.
I think there are some of these in Canada, but the concept doesn't seem to have gotten across the pond. It might actually make sense.
I think there are other things pro for same day, like lowered infection rate and that kind of thing. You are probably less likely to get a nasty hospital staph infection. Another thing is that moving around is good for you, short of raising your heart rate. I walked around a LOT. Didn't do anything greatly vigorous but being in a hospital connotes being incapacitated.
Most same day surgery centers are connected with a hospital, so if you get an infection (or other serious complication) you could be admitted, if it were necessary. I'm sure ,say, Dr G has admitting rights to the hospital that is next door to Memorial Same Day. I've never heard of anyone getting admitted, but I heard that there are guys he must do in the hospital-- for instance if you had a serious medical condition. (I saw a video of someone who had gotten hydrocephalus treated which involves shunting fluid away from the brain.) I have never read that you are usually in any serious danger after top surgery. It isn't exactly trivial but it's not like heart surgery either.
Most people are not in a terrible amt of pain, so I don't think most surgeons will use drips and so on. Most of the time you are given a prescription of Vicodin or similar drug. Frankly I didn't even take the Vicodin and know many people who maybe took 2-5 of them max. I know a couple guys in the UK, and they took some prescription pain meds (no drip). Top surgery is more uncomfortable than out and out painful, imo.
You wouldn't need your bp and so on taken actually. But since you are in the hospital they are going to justify you being there by doing it. If they didn't do it, they would have a hard time explaining themselves to the local health care boss.

--Jay