Couldn't agree with this more. I was privately educated, and have taught for over 20 years in both systems, currently as a head of department at a state grammar.
There is really no comparison, neither system is bad, both have good points, I'm extremely proud of the school I work in, and if I was solely concerned about academic outcomes would send my child here.
However, private school offers so much more than just lessons, there is so much in the way of sport, outward bound, societies, arts, drama, extended curriculum etc that doesn't top and tail the day, it actually forms part of the day to day routine.
The old boys network is strong too, not in terms of financial backscratching, but just keeping in touch, I'm still in regular contact with all my classmates - and if I wear my old boys tie, as often I do, I will often encounter other private school alumni from other schools, it breaks the ice.
Then there is the history of the places, the atmosphere, it's really hard to quantify, but they are just in no way the same, and unless you have been a pupil yourself in private, I just don't think you understand.
So my lad is off to private senior in September, £40K a year (£50K with VAT!!) but well spent in my opinion.