I don't see how people cannot have the desire to go to one of the world's top universities? You get the opportunity not just to learn from and work with top academics in your field, but also get the opportunity to make lots of connections and contacts with important people both in academia and industry. A degree from any Russell Group university is always going to put you in excellent stead for the future, but I think that Oxbridge will always be the icing on the cake.
What you say is partly true, but isn't limited to Oxbridge. They're not the UK leaders in a lot of fields, so it's not the case that all purely academically driven people would put Oxbridge first above everything else.
There's also the fact that not all people want to go to university for the academic experience, but that's perhaps symptomatic of the state of higher education in this country
