The publisher does not have option to provide other DRM free formats. Imagine that in the future you bought a device that has 10 inch (or more) screen that is capable of displaying PDF formats just fine, or there is another format that let the publisher attach multimedia, or you bought other device than Kindle. You would have to purchase that book in new format somewhere else. Just other publishers and their stores support that now much better. Just look at the example of Oreilly that I have posted or below:
http://www.teleread.com/drm/amazon-s...a-little-hope/
Maybe I should restate the whole post saying to support multiple DRM free formats.