Aside from triples, I also think that part of the misconception that soo many skaters are landing all their doubles, is because you show up on an average high freestyle at a mid-level rink and you see the ice filled with people doing doubles left and right - but those are the same 15 people that are coming and skating 2 sessions 5-6 days a week, so they are just ALWAYS there. It's not that so many people as a % of skaters are able to do them all, just a lot of people as a % of people you see at the rink are able to do them all. Even 'just' doubles, it takes practising almost every day to maintain the ability to do them at will.
I think the same thing applies to year over year analysis. Say for the sake of argument that there are 200,000 skaters in the US and 2,000 of them do triples. That doesn't mean that a beginning skater has a one in 100 chance of learning to do triples. There is significant turnover in the 200,000 skaters year over year, but those who do triples would tend to continue for many years.