I've created an article and submit it to article directory then if I search for my article it shows supplemental results. Does it mean that I have duplicate content even the article is mine and posted on the other site?
IMO, If there had been a chance of a duplicate content issue with article submissions, all the major article submission sites have gone off the search engines. Each article they publish will also be published in many other sites as well.
I don't think article submission can be considered as duplicate content as google might be viewing article & Press release differently.
I think they see the dupes but for relevant sites it is not completely devalued. I think in the future when article marketing gets out of hand Google will discount the links. But for now its a great money maker for SEO's and it works great for the client.