Thank you Andy. I appreciate the comment regarding more styles especially block quotations which we have been working on in MDL-45662. This would be another way of addressing your need, but it will not make it in until at least 3.0.
There are some reasons styles in the Atto editor are a little sparse. It is meant to produce text that is easily read and understood on the web in various contexts and with various applications. This means that text is formated mosty with HTML tags rather than CSS. Adding CSS classes would have to be supported both in the theme and in the editor. Text that is cut and pasted from Moodle into another application might lose the intended formating when it is transferred.