Meh
I doubt dedicated ebook reading devices will go away any time soon. It's certain that other devices that can read ebooks will be introduced; it's even possible that numerically, most people will use a multi-function device instead of a dedicated device.
However, to presume that means "ebook readers are doomed before they take off" is a fundamental misunderstanding of the dynamics of the book market, as well as several technical aspects of ebooks and electronics in general.
• The majority of the public only buy a handful of books each year. However, a smaller percentage buy 10 or more books per year, and represent a key segment of the book market. These are also the users who will benefit most from a dedicated ebook reader, due to ease of use, less eye strain, fewer distractions, longer battery life etc. It's likely this segment of the market, as well as the education market, will support the market for dedicated readers for quite some time.
• Unlike video games circa 1983 (or 2009), most ebook formats can be displayed on a multitude of devices. E.g. B&N makes reading software for PC, Mac, Blackberry, and iPhone; buy a B&N book, and even if you switch to a tablet PC in the future, you're almost certainly covered.
IMO format isn't a big issue. People have dealt with incompatible standards and formats for awhile now; I don't hear a lot of fear and confusion that if I buy a Wii game now, I won't be able to play it 40 years from now on whatever is around. (And yes, some people do enjoy playing
old video games....)
• Old electronics may fade away, but they don't die quite as swiftly as most presume. E.g. you can still get a good portable transistor radios, despite it being "ancient" technology by some standards. And in many cases, focused devices still offer numerous advantages over multifunction; digital cameras will be around for a long time, despite the ease of putting a halfway decent camera into a smartphone.