What' the difference between Wiki 2.0 and article submission site. How does Wiki 2.0 help in Search Engine Optimization?
On web 2.0 sites you can create blog, which may not need moderation while article directories for article and most of the article directories go through moderation.
Wiki 2.0 refers to a platform that enables websites to be dynamic and collaborative and allows users to work together and become part of a topic discussed via their comments, suggestions, reactions and/or the ability to edit out some parts of the discussion. So, users are able to develop a web page based on their own needs rather than be passive and just read what web pages creators are writing. On the other hand, article submission refers to articles submitted to article directories either for recognition or link building purposes. Once submitted, users have just to read it without having to edit it out. With regard to your other question, it is somehow similar to other link building techniques wherein you can include a link of a certain website.
Article directories have been so devalued these days too, that some would argue they don't even deserve a place in a 2013 SEO campaign anyway. WebDev