A note on Google and PageRank:
Google is biased at least partially, few years ago they found out and admitted on their blog that PageRank no longer is effective. It could have exhausted even their resources to calculate PageRank regularly for trillions of pages along many quadrillion page intersections, they probably didn't put into account or expect the web exponential growth in recent years. This cumbersome process along the extensive work of SEOs made them think twice and gradually changed the algorithms to something extremely non-scientific and experimental which surprisingly worked as good as the original idea. However in this process some websites happily accepted the results their business thrived and they prosper, some eliminated or got an unfair treatment and never came back. Since then no one knows what exactly Google is doing and that is the concern since nobody knows what portion of the web is missing or hidden from users.
Twitter is a successful business model not for the complex algorithms or UI or anything in that nature, it is successful because "everything" chronologically appears on the search with almost no manipulation. I believe it was the most important factor that made Twitter so popular and let it capitalize on Google manipulative system.
Good to note that the PageRank original concept is completely in contrary to the requirements of the real-time search, older an article is, more likely to accumulate external links, therefore PageRank tends to give higher scores to older pages and vise versa new pages have almost no rank.