The old default android browser was so much nicer than Chrome in this area; you zoomed in until it was comfortable, then double tapped and the text, not the whole page, would reflow to fit horizontally.

Yes, all things considered, I'd say providing the ability for consistent font size increases on mobile will correspondingly provide an increase in ones userbase or readership.

Not sure what you are referring to, but that sounds like a symptom of the web developer setting absolute sizes for some fonts (12px) vs. relative ones (medium).