I am doing research into social media sites, and one thing I have noticed is that most of the main players in the social media and communication world (Facebook, Twitter, LinkedIn, Microsoft, Google) all have their registration forms/sign-in pages on the right hand side of the page.
What I don't get is that I have been taught that generally, the most important elements on the page should start top left of the page (in Western terms). I know this maybe wouldn't look as good, but was just wondering why forms generally are on the right of the page? Any particular UX reason, or is it just a design convention that was started by a particular site?