It seems from this - entertaining - discussion that the majority of kindle peeps, at least those represented here, don't care what format the book is in. Maybe it's just me!
I like changing fonts for each book I read; using a handwriting fonts for diaries or letters, an informal font for comedy, and a heavy, dark font for gothic novels.
Perhaps this isn't important to others.
I'll continue converting epubs into azw3 for my own amusement. To load any onto mobileread I would have to strip the blurb and covers (nicked from other sources, probably copyright).
If newbies ever ask, "how do I use custom fonts?" or "why will only certain books use custom fonts?" here's me saying "I TOLD YOU SO!"
(Poor horse!)