Thomas Edison is often quoted as saying, "To [heck] with the rules. We're trying to accomplish something here." Well, that quote doesn't apply to e-book formatting and for a very good reason.
Question: "I've written my book in several different fonts and styles, but Amazon and Smashwords rejected it. Why can't my book look the way I want it to look?"
Answer: The answer lies in two areas.
1. Most of the major e-book formats are based in HTML coding, which can be a tricky minefield to navigate. In some cases there is no HTML coding for the style you might want to use, and so when the file is converted to Kindle, for example, the style you created will default to either a normal paragraph style or maybe something that looks even worse.
Another thing that's tricky about the HTML based formats is that sometimes a style tag isn't closed properly and this can keep your file from passing .epub validation. See also my blog post on The Sytles and Formatting Palette Isn't Necessarily Your Friend.
2. E-readers are just like our computers in the sense that not every device comes pre-loaded with every font that was ever created or a way to view the 1,000s of fonts that are sold or distributed as free downloads.
I often receive files from authors who have used fonts that I don't have on my computer, and guess what? The font defaults to Courier. Most e-readers use what are called Base14 fonts. Base14 just means standard fonts such as Times New Roman, Arial and Courier.
Until e-reading devices evolve to the point where a book can be formatted with all the creativity of a print book, we have to—with apologies to Mr. Edison—follow the rules.