If you look at it as B&N vs Amazon, yeah Mobi would look like the clear winner, but the thing is, it isn't that clear cut.
And yeah, I think dedicated readers will eventually die out, because if you look at things in the long run, that is always how it is. Who uses a calculator anymore? Outside of school, most people use computers, cellphones, etc. General purpose devices always win out in the long run, because to the unwashed masses they're "good enough".