Web 2.0 is not dead, the speed of page indexing died. Notice that google is working every day to fix spam issues and it doesn't always want to index the page.
Just think how can google bot get to your Web 2.0 page which is in no way related to the sites. Imagine someone in a store put some product behind a closed door, how can a customer buy it if no one shows it to him?
Use link indexers.
Web 2.0 is not really a quality thing, these links do not get fed from the primary domain and use this method is only based on cheating google, when he sees the overall value of the domain and this link is considered a step better than a link from a zero site. Only a unique and high-quality text gives some value to this article
"Just think how can google bot get to your Web 2.0 page which is in no way related to the sites"
i usually use tiered link building, i.e. other web 2.0's & blog comments etc below them.
"which is in no way related to the sites."
they are related to the sites they are linking to, it is the same type of content