Kindle for PC (Win8) — Bug or Feature

This is a bit technical; forgive me.

So, the Kindle app for Windows 8 doesn’t seem to accept “personal” documents. That includes the PDFs and such that one can read on other Kindle platforms; it also includes .mobi files sold through retailers other than Amazon.

Bug or feature?

If a bug, how badly do we want them to fix it?

If a “feature,” do we think that we’ll see it spread to other Kindle platforms? And how can we discourage that?

I’m a little worried — as someone who sells Kindle-compatible .mobi ebooks on other sites (including my own) — that our monopolistic friends are closing the sandbox.

Anyone else have any thoughts?