That doesn't change the fact that Apple is ignoring the published standard.
If that's what they want to do, then they should call it a proprietary format and let people choose whether they want to use it, not have their cake and eat it too.
Good point. Does the standard insist on the specified fonts, or are clients allowed to overrule them according to user prefs? If the latter, a fix is just an additional "book default" entry in the fonts menu.
(If the former, that's a lousy standard, right there)
The standard doesn't do anything about specific fonts. The standard DOES have facilities to set a font family, i.e. serif, sans-serif, fixed-width, etc.
It throws off formatting for a lot of books if you screw with that sort of thing. Which is what Apple is doing.
If that's what they want to do, then they should call it a proprietary format and let people choose whether they want to use it, not have their cake and eat it too.