See, that's exactly what I thought. Until I get tired of having to wander round all the Epub sites checking if the book I wanted was a) available and b) cheaper. And then having to contend with using Adobe Digital Editions. And not being able to easily transfer a book from my reader to my wife's or my iPhone. In the end, for all its openess, Epub just ended up being a whole lot of hassle.
I wanted to hate the Kindle. I much prefer my Sony PRS-505 in terms of hardware. But the Amazon experience is far, far superior - no faffing about with checking prices for starters. I'm not one of the folk who think ebooks should only cost pennies, so if it's the same price as physical, or less, I'm happy. Buy the book right there on your Kindle, or via the website and choose which device(s) to receive it. To send the same book to another device, just go to the website again and resend it. And as for the whole "wireless bookmarking" thing - so useful, if not essential when you read the same book on multiple devices (e.g. on the e-ink reader normally, but on a phone while standing on a platform / waiting at the Post Office etc).
I really hate to say this, but in my experience the Kindle just... works.