Welcome to the forum aab24!
Without boring you with technical details, ePub books use HTML to control how the ePub is displayed on your reader. Each reader then interprets the ePub's HTML and displays it. But like various web browsers, the different reader devices don't all interpret HTML alike, so there can be device related differences. Also some reader devices override some HTML formatting. However, in your case I think, as others have said, that the issues you are seeing are related to how the publisher formatted the book and/or how calibre converted that formatting.
Unfortunately there are way too many book publishers who do not understand the HTML concept of reflowable text. They are still stuck in the print on paper style of publishing where they strictly control everything (text and style) that goes onto each page of a book. But of course ePubs are designed to be like web pages where the publisher controls the text but allows the person reading the text to have some control over styles (like font, font size, colors, text layout, etc.). Publishers are slowly, very slowly, catching up with the digital age of reflowable text.
Another unfortunate circumstance is that many individuals (as well as large publishing houses) have little or no concept of how to create and format reflowable text. So it is possible to get an ebook that is nearly devoid of formatting. I think that is what happened in your case.
Last edited by jswinden; 05-24-2011 at 12:41 PM.