We started using private because our catchment school is failing and has bad Oftsed results.
We also chose it because it goes from nursery all the way to 18, so dd started at 7 months and is still there now at 6. DD2 is now in the nursery too.
Other reasons - she's one of 10 in her class. I think that's important. The school has a real 'family' atmosphere with the older children encouraged to look after the younger ones.
The fees are pretty much the same as I was paying for nursery.
Jobs of parents in dd's class - probation officer, Virgin tv installer, teacher x 3, HR Manager etc. No one seems to be 'rich'.
Our house is a 3 bed semi in a not great area, cost £140k 6 years ago.
Wages - mine are around £10k over average part time, dp's are around £5k under average.
So we do afford the fees by having an old car, a house in a slightly dodgy area, no holidays etc. Is it wrong to say that? Is it still bingo if its true? 
I feel really sad that you can only have the choice if you have money. Seems wrong. But I'm not going to send DD to a failing school because the system is inherently unfair. Does that make me a bad person then? 
If you genuinely think your local state school is bad, could afford to go private but don't because of your principles then fair play to you. Well done.