It all depends on what is in the style.css. For instance; if you don't have H1 defined in your CSS, all of the editors are going to style it according to their default.
A quick check, how do you define your default font for your site? Most of the provided skins define it in the body selector:
body {font: 70%/1.5 Verdana, 'Trebuchet MS', arial, sans-serif;}
If you are defining the font with a unique selector, the editors aren't going to know that.
-Joe D.