This site has classifieds on the right hand menu. It has functionality specifically for ads which forums don't do (such as consistant format, pictures, auto-expire, keyword notification, etc.).

FTE is a content site, not a flea-market. Many, but not all, sites that have the classifieds in their forums have little else to offer other than forums (such as the Buick site you mentioned) and classifieds offer an easy way for the webmaster to get post counts up. FTE doesn't need that, I'd rather have ads expire and disappear.

Also, if someone is selling enough stuff to merit feedback, then its a part-time business and they need to pay to advertise here. If they are going to make a buck from FTE its only fair they pay for it.