Wimbles101, what you say is partially true but also very incomplete. In the real world most people have to get a job, ideally with a "top" company. Companies have always used universities to filter their candidates for them. Top universities filter for academic achievement.
I have worked for multinationals in both the US and the UK, the kind many of you would recognize as being at the top of their fields. I can tell you that, when hiring into professional track positions, the kind with clearly laid out paths to the top, we mostly recruit from very selective universities. We understand we're missing out on some very high potential kids who didn't succeed academically in secondary school but, quite frankly, it's not economically efficient to search at every university to find these kids.
It's important to keep in mind probabilities and expectations as well as anecdotes. Most people know or know of some child who got a place at a highly competitive grammar with minimal or no preparation, just on sheer ability. These children do exist, but they are few and far between. Most people know or should know that preparation for the exams improves the chances of getting a place for nearly all children.
Similarly, many people who don't go to Oxbridge will get jobs at Google or Goldman Sachs. But you should know that your chances of getting the interviews and, therefore, the job, improve greatly if you do have Oxbridge on your CV.
Some people will fare poorly at academics but go on to succeed spectacularly in many ways, including financially, e.g., Richard Branson. Some people will have Henrietta Barnett and Cambridge on their CV and not have success in any particular endeavors. But when you look at the whole population, it's pretty clear that academic success is highly correlated with subsequent financial success.