If you enable showing the description for the links module you can add free text description after the link including graphics. This would be in addition to the text link rather than instead of it, but text links aregenerally more accessible. However as you have found you can do pretty much anything with the html content module so if you want graphic links without text links thats probably the way to go. Links module is just a convenient way to make a list of standard text links.

Best,

Joe