Your articles don't get recjected if they are not exclusive, but you do infact get paid less on the upfront payment of the article (if applicable). I've found that it's generally only $0.25 - $0.50 less for the upfront payment, so if I submitted an article as exclusive I typically get $4.75, and when I would submit that same article for non-exclusive the upfront payment can be as low as $4.20.
It all depends on what you want to do with your article, but I almost always submit mine as exclusive.