How well do your current pages support Lynx?
Does that answer the question?
And how much code is there that is IE6 specific that IE7/8 isnt compatible with?
It's not so much a case of code not being compatible with IE6, it's more that IE6 botches layout.
You can create a perfectly accessible, standards compliant site (that looks just fine in Lynx), but in IE6 will have broken backgrounds, weirdly positioned bits, overlaps of boxes etc.—in short a site that looks terrible to the user. The developer, who would like users to perceive their site as looking nice, rather than a broken mess, then has to spend time (sometimes a lot of time) trying to pin down special site-specific IE6 fixes (that sometimes aren't standards compliant) to make IE display the site the same as all the other browsers manage to.