I too called Sennheiser a while ago asking about the difference and was told the same thing they said to you....but that's not the fact according to myself and many, many IE8 and IE80 users here at HeadFi. We all hear (quite) a difference between the IE8 and IE80. They are not the same sound wise. (Maybe this is because of the Stainless Steel trim plate on the IE80?)
If you are 'only' concerned with massive mid-bass then you will probably like the IE8. If you want less bass and clearer mids and highs then the IE80 is better.