[MrZongle2]

A book certainly is just a medium, but it's a particularly accessible and durable medium.

If you place a 50-year-old book written in English in front of me, I can immediately pick it up and begin reading. Books far older than that are equally as legible and, with care, accessible.

What are the chances that in 50 years that even half of the current ebook formats will be viewable by contemporary technology?

This isn't to say that other formats shouldn't be used or improved, but we have yet to see a medium that is as unfettered and easily used. It's hardly about nostalgia.