Totally agree with most of the previous posts. I went to Cambridge, DP to Oxford.
They are just universities. Now, in the working world, I realise that Oxbridge students are among some of the least-prepared for 'ordinary' life. They are unable to take term-time jobs, and frequently use their highly academic brains in ways that simply aren't commercial.
Sure, it sounds like an ideal place to go but I only went punting three times, and soon enough you stop admiring your surroundings and start worrying about the three essays you have to hand in and how the hell you';re going to learn middle English in a month.
If I had my time again, I'd definitely go back, but can totally see the merits of going to a London university, or perhaps not spending my life on a rollercoaster of work/sleep/booze in which work seemed to encroach on the other two areas 90% of the time.
They are just universities, and by suggesting to your son that he has failed by not going there, you're doing him a disservice.