Toby, may I correct you there.
I worked in a Private school (though called Public, preferably) and yes there is a business side of things without a doubt.
But there is certainly more sport, more outings, more drama and better food than at state schools. This has no bearing on academia, but on the wellbeing of the child.
Also, with all these blasted SAT's etc, I would argue that state schools are running a greater risk for results that Public schools.
If Eton has a really bad year, it will still be there next term.
If Cardiff Secondary for Smeggy Children fails beyond its usual failings, it may well be closed next year.
The pressure for state teachers is therefore very hard.