All the other tablets I've seen prototypes of have a 16:9 display, whilst that means nothing as such, it does mean there are people out these who are interested in other options.
The Notion Ink Adam being one model that some are interested in.
Other tablets are 16:9 for the same reason they have USB ports and run Flash and/or Windows: to distinguish their product from Apple's by catering to complaints and ticking boxes... prior to figuring out whether these are good design choices or not.
Would the OP (or other widescreenies) like a 16:9 display smaller than the present one?
You'd get lighter weight and more battery life too... would it be worth it for no black bars when watching movies?