If you're out of step with the universe, then so am I. I agree with you that even margins on both sides looks much better and that's the way I do it for blockquotes. Even on my 5" reader, there's no reason to not center the blockquote with even margins on each side... you don't need a huge indent on either side, just enough to set it off from the rest of the text. Quite often, the text for a diary entry or handwritten note is also italicized as well, and I'll often do both to match the original book.
Same when I run across the page with all the publishing dates and they just have it all left aligned. Pick up a book and that page is just about always centered, at least I've never run into one yet that wasn't centered. Yet a lot of ebooks are just left aligned for that page which looks like crap to me and I think is just lazy formatting.
Now if the thought is to make it acceptable on all reading devices, including cell phones, maybe there is some argument to just left indent. I'll test my epubs in various font sizes and styles, but I really don't worry at all about how it'll look on cell phones. They're just too small and I think you're going to end up with parts that look bad on a cell phone no matter how hard you try. So I'd rather go for good formatting for ereaders.
When I'm in doubt, I defer to how it looks in a real printed book.