"Yes, but having the argument during labour when she is begging for pain relief is not the time to educate her in such matters. It should have been part of her care and preparation months before hand and the birthing environment should have been set up to support that." - Oi! I said that first!
With regard to the information that women are given, I was given very little information of use. In fact the hospital 'preparation' classes put the fear of God back into me so I refused to attend more than the first one. So I know first hand that the way the NHS prepares women for birth leaves a lot to be desired. I also know that the information which can transform a woman's approach to labour is readily available and can be easily accessed. So there is no excuse for the NHS preparing women so badly.
However, I do believe that pregnant women should not expect everything to land on their plates - precisely because pregnancy, labour and birth are such individual experiences. I purposely sought out good information which enabled me to overcome my terrors. The women I have heard saying they are not going to prepare are just as well-educated as I am, and just as capable of seeking this information themselves.
You mentioned the position of the baby/ size/ mother's health as potential aggravating factors which can negate all the best preparation in the world. Of course there are exceptions to the rule, it's the same in every aspect of life. But if a significant proportion of women - the majority, even - can be assisted in managing labour pain with better preparation, the outcomes will likely be better all-round: better for the mother's body and overall experience and memory of the birth; lower cost to hospital; shorter hospital stays - benefitting mother, child and NHS budgets; I'm sure there are more points that I can't think of.
I don't know what happens to women for whom an epidural doesn't work - CS, perhaps?