It has nothing at all to do with fiction vs. non-fiction, I have a Kindle that I love and adore, and I read both fiction and non-fiction on it, and both are wonderful experiences.
What I don't read on it are PDFs, because the viewing experience is horrendous with PDFs. I've just started a degree programme and I've got loads of PDFs to read and I'm looking for a device on which to read them. I'm hoping that Apple do an iPad Mini with an excellent display that I can view and read with ease PDFs. The form factor of my Kindle is actually perfect, and a smaller iPad that could still display well PDFs would be the ideal product for me. The regular sized iPad is just too large, and doesn't really complement my other device, an 11" MacBook Air.
If Apple doesn't release an iPad Mini, or the one they release doesn't meet my screen resolution requirements, I'll look at the Kindle Fire HD (or Nook, which has an even better screen). If none of those work for me, I'll then go back and look at an iPad 3, but it'll be a last resort - it's just too big for my needs, I'd like an iPad 3 in the form factor of my Kindle, which I find perfect.