While it may be technically true that ePub offers publishers greater control over format than mobi, my experience is that Amazon formatted books are almost always superior to the epub versions I buy elsewhere. On a couple of occasions I have purchased both commercial DRM versions of the same title just to see for myself.
Also, outside of a handful of vocal folks here at Mobileread, I have never heard these claims elsewhere. Until it matters to consumers -- and if I were Sony or Barnes and Noble or Kobo I'd be demonstrating this "advantage" daily -- it won't have any impact on ePub vs mobi.
As a former typographer, I assure you I care about such stuff. But, as ePub does not live up to this technical promise, and the "inferior" format which provides a better reading experience and continues to innovate meeting consumer needs as they evolve ... this so-called "inevitable impact of superiority" is irrelevant.