Well, Kenny, actually Apple
has won the online music market.
Don't get me wrong - I personally do like ePub and openness, and that's why I bought my Opus. If I were buying a new reader today, I'd probably still get an Opus. But I'm not a typical consumer (and nor are most of you.) All of the computer-level fussing that's required to use a device like the Opus is well beyond what the typical person is willing or able to deal with.
Yes, sure, someone else can duplicate Amazon's set-up. Maybe Sony will get there eventually, but ironically, where I'm sitting at work, I can't even contact the Sony bookstore because their software isn't capable of navigating my proxy. So they have some distance to go.