I second Kenny Buckles: the web version just takes the HTML from the email and renders it on a webpage.
While emails resource to tables and other elements to circumvent limitations or some systems, such as lack of background images support in MS-Outlook or supression of paragraphs in Yahoo, browsers often privilege divisions (div) and cascading style sheets (CSS).
Campaign Monitor has good suggestions for portable content. It is important to keep in mind Marketo templates have the mktEditable tags, a non-existing feature in generic templates.
Extracts of the HTML source would be helpful indeed.