Not just DRM. Making locked up software on a platform like Linux is just a pain. You'd have to check and verify all distribution/CPU platforms (as you can't trust the community to do this for you). This in itself is one of the major reasons proprietary vendors don't go linux. It's too small of a market, requires too much effort, and in the end, you will be pi**ed upon because you're not open. Also, the developer-to-user ratio in linux is abnormally large compared to windows land and the LIKE to hack and make/break stuff. Sending in a DRM piece of software in there is just putting their heads in the lion's jaws - and to make matters worse, a DRM crack could then potentially be used in other, more 'accepting' and benign platforms.

This applies to kindle on Windows. Actually, the one that makes sense here is Windows Mobile. Largest user base, used to micropayments, small number of hackers compared to the nomber users... Why bother with linux if you can go to such a market ? There are simply largely incompatible business models at play, and that's why DRM doesn't fit open platforms. Remember, you you want the content, not DRM per se. It's just that the publisher is forcing you through DRM hoops as it is part of it's business model.