I believe kf8 format does break correctly around em and en dash on all devices that support it. And there's always been a decent workaround, for sufficiently diligent ebook creators (of which there are a few), i.e. insert zwnj character:
Also I do see sparing use of hyphenation on Kindle iPhone app (which still does not yet support reflowable kf8 BTW). I'm guessing they are just subclassing iOS objects and those in turn are probably using webkit, which supports this behavior.
Nook and Kobo get hyphenation by virtue of Adobe RMSDK, I think it has been there at least a couple of years now. Sony either is still using something older or has disabled it.
I do like hyphenation myself, if it is done 'tastefully'. But like 7hir7een I use small text sizes so things tend to justify well without it. At larger text sizes the same effect can be had if you put it into landscape.
I think Amazon will eventually get around to adding this. But it is not 'free' and it will be another thing that diligent ebook creators will need to take into account (e.g. to prevent hyphenation of headers and delicately formatted poetry from breaking in the wrong place). And some people will hate it and want a way to turn it off.