"There's a wonderful synergy in that case, since Oxford and Cambridge appear to think that these students aren't intellectually exciting enough for them either."
Hmm, that's a bit snarky, if I may say so.
Its not as if there's a cut-off point for "intellectually exciting." There will be students in just about any uni anywhere who will be more "intellectually exciting" than most of them at Oxbridge.
Just as the top schools hardly have a monopoly on the most academic, well, nor does Oxbridge. It's exactly the same thing, just a few years down the line.
Of course there will be super "intellectually- exciting" DC in all comprehensives and just about any school in the world - as many as exist in the general population. But that doesn't mean students at Westminster etc are any less "intellectually exciting." It's just a process of selection leading to a greater concentration of very able students in certain schools and they work bloody hard to get in there in the first place. Nothing is a certainty in terms of admission - just like Oxbridge. In fact, in terms of numbers, competition can be more intense to get into top schools than it is to top universities (relative to age of course).
And yes, I can think of quite a few who have gone to MIT or Harvard having also been offered Oxbridge.
Some seem to like the idea of a broader first two years and then "majoring."
I have no experience of US applications personally, but it definitely looks like a totally different and very exhausting process, based on what I've seen with DC friends. The way the personal statement is written is totally different and it seems like every uni has its own requirements for this. Sometimes it's a random essay question, so they may have to write about five essays for as many applications. They also have to tick far more boxes - eg. a sport at a high level; involvement in charity / community work; evidence of leadership; etc etc - many "broader" qualities that Oxbridge don't really care about. Not to mention SATs and ACTs. People start planning for US applications much earlier because you can't suddenly produce all that extra-curricular 'evidence' last minute. They've often been at it for many years, building up a kind of 'portfolio.' It's like you have to sell yourself as an 'all round' product they want.
The way I see it, if you are talented in a sport to the extent you do it at a national level, such as HoneyMobster's DC, why not use that to your advantage if given the opportunity? Some DC are just like that and want a broader experience. DC friends at US unis get points that go towards their final grades from their extra-curricular involvement. It's not optional there.
Also, apparently hardly anyone pays full fees as there are so many scholarships for all kinds of things that just don't exist over here. People that would never in a million years qualify for financial assistance here, are getting bursaries because they meet some diversity criteria or something else they never realised they were eligible for. Rowing seems to be a big one - people get full ride scholarships when they weren't even in the A team for rowing. Also "soccer" players are another fave and I know two girl "soccer players" who were offered scholarships for this and went because women's soccer is a bigger deal over there. So many factors.