they are very picky about the sites they add, if its related to the category and has no ads, and it has been live for not just a couple days, then it gets added
the only way to get links in to stick is to either become or befriend a really trusted wikipedia editor. If that wikipedia editor (not yourself) is convinced the link should stay up - it will, and if it's deleted, they will put it back up for you. But doing it yourself is not likely to work in most cases.