At least they finally started allowing you to ignore the publisher-preferred font in recent years. Some books published that way were illegible and it's obvious that Amazon employees do not use their own products.
It's a fine line. If a reader goes too far in overriding default fonts, you can have readability problems with things like drop caps. Same goes for overriding the font color (e.g. forcing the color to black could result in black-on-black text if you have an inverted-text decoration at the top of a chapter). And some manufacturers' devices annoyingly override fonts by default, which results in a diminished experience in books that use different fonts to convey meaning (e.g. computer books that use code font for symbol names).
IMO, what we really need are standards that all the reader vendors agree upon, including:
- A set of rules for when styles do and don't get overridden by these vendor overrides
- A ban on use of the universal selector in vendor overrides
- A requirement that publisher fonts be enabled by default until the user explicitly overrides the font
And so on. Then again, half the readers ignore large swaths of the CSS specification already (and probably the HTML and EPUB specs, where applicable), so I cynically wonder if they would just ignore these sorts of standards, too....