Yes, you are right WMST, those people who choose private primary ed initially do learn more about the system because they are in it.
That's one of the reasons I suggest to people on here that if they aren't sure they can afford to fund private ed from 3-18 or 5-18 and then university, they should think about using spare cash to buy in extras to build on the state education e.g. music lessons, join the local hockey/rugby club, take tennis lessons, etc. All of that builds on the skills of the child.
Today it is easier than ever to find out more about the education options available, including scholarships and bursaries, because of the internet. Almost every independent school will list its fees, entry requirements etc on their website - parents don't even have to summon up the courage to ring and ask for information or worry that the person on the other end of the phone will be secretly laughing about their address and wondering what on earth makes them they'd fit in.
And although you may think it's all about preparation, I've been assured that the staff who do the entry stuff are perfectly capable of 'sniffing out' the genuinely talented pupils. In fact, one local school, so I have heard, interviews every single applicant BEFORE they take the exam and will not necessarily take, say, the Top 100 candidates if there was a problem perceived at interview.
I really do wish more people would not be frightened of taking the step if they are genuinely interested in private ed, even if they don't think they can afford it. If they're not interested, then fair enough, but they should leave those of us who choose it to get on with it and don't criticise our choice of how we spend our money.