do you believe that the quality of a join can vary?

we all know traffic quality varies, so does the quality of the join that the traffic generates vary as well?

case in point: i get joins to sites that stay anywhere from 4 to 8 months... an affiliate sends joins that never last more than 3 or 4 months... if both of us had traffic that was good enough to convert, why don't the affiliate's joins last longer?

its an odd phenomenon i think, but i truly believe that join quality can vary with traffic type...

discuss...