Originally Posted by HarryT
The basic problem is that, unlike Mobipocket, the ePub file format does not define a dictionary format, so every reader manufacturer has to "reinvent the wheel". This is, IMHO, a serious flaw in ePub. With Mobipocket, on the other hand, dictionaries are defined by the file spec, hence you can buy a dictionary in the bookstore.
In theory you're right, in reality it comes down to one manufacturer-one dictionary with Mobipocket, too. Mobipocket dictionaries can only be used by devices that use the Mobipocket Reader as the basis of their reading program. And I don't know of any manufacturer who Amazon granted the right to implement the Mobipocket Reader in the last years (Bookeen and IRex and others were before). Your Bebook Neo is well able to read Mobipocket files but you can't use a Mobipocket dictionary with it, you have to use the device's dictionary. The same is true for the Pocketbook readers.