I think part of the reason people think it's brave to plan for a natural birth is because there's a point when almost everyone would take pain relief if it was offered. And maybe those who have given birth at hospital and did accept pain meds feel like they really, truly could not have done without them. Or maybe they feel a small twinge of guilt or inadequacy for "needing" them, when others have gone without. I know that with many of my deliveries (four of which have been med-free) there was a point (usually at transition) where I'm not sure if I can handle any more, and if someone would offer drugs, I'd probably take them.
I have to say that in my first delivery, I definitely felt like I needed pain relief. I was overwhelmed, panicking, and not coping well. It was a fast and intense labour. So when I hear a first time mum say that she wants an all-natural delivery, one half of me is thrilled for her and knows she's making a good choice, and the other (silent!) half of me is thinking "oh honey, I hope you've got some support to help you though this, 'cause it really is hard!"
I think a lot of first time mums dream that they'll sail through labor strong and silent and stoic, and aren't really prepared for the challenge that labour presents. Then, as they struggle to cope when labour becomes challenging (and it IS challenging!), they feel like an epidural is their only hope. If they knew what they were up against - realistically, without horror stories, or glossing over of the real challenge of labour - they could prepare better with alternative coping options and the support of a doula.