I have used Smashwords for years. It's good for fiction publisher, not quite as good for nonfiction. And it's only for e-books. All the options I share in this post are good for authors who want to publish print books. Today, it would benefit most authors to publish in both formats. I've never used Draft2Digital, though I've heard other authors use it with great success, but it's also for e-books. Another e-book distributor option is BookBaby.
I'm glad to hear about your success. You're talking about 40K in royalties on Smashwords for nonfiction?
Sorry, I wasn't clear, nor did I fully comprehend your post it seems. The KDP reference was throwing me, as when I was still writing Createspace was for print (they hadn't been sucked into KDP yet).
Most of my royalties came from fiction, and that's spread around several sites. Ironically, KDP comes in fourth (behind Smashwords, D2D and Nook direct). D2D does offer print on demand (I haven't used it personally), however it is up to the author last I read on it to get the books listed on the platforms. Nook was also beginning to allow print for the B&N bookstore as well when I stopped writing/publishing.
Ah! Got you. I could have included the history lesson and purchase of Createspace by Amazon.
Fiction does seem to do better among the indie author crowd, but I think that's going to change. There are a few indie non-fiction authors starting to shake it up, but I think there will be more. There are so many POD options now, and POD author-publishers can sell their books through any channel a traditional author can sell through. I was particularly concerned about your figures on Smashwords because if you look at the top seller list, it's dominated by romance novels. There are a few non-fiction books, but they're more the exception than the rule.