Experience. There is a tool TinyMCE which will plug in to a DCT and will allow users to write HTML in a WYSIWYGI almost never use that because proper definition of a DCT/TPL/XSL set will limit the need for HTML.
Very true. I liked the (very) old templating UI that allowed bold, italics and underline and that was it. Of course you can do that with MCE and VFE as well.