Originally Posted by kiwidude
I don't know the history, but I will say that it could be the MOBI format has something to do with it (particularly if the book was a conversion from mobi). Since MOBI has no right-margin capability, and will format the document internally with blockquote.
well the sigil button for increase indent's default value may also play a small part
it could well be that I'm seeing it a lot in free Kindle book conversions, but I'm sure I could dig up genuine retail epub examples also - pretty sure the recent humblebundle collection contained some examples.
Maybe folks authoring for both kindle & mobi opt for something that works in both?
I expect Hitch will be along shortly & wil tell us how it should be done