The biggest asset companies have today is their customers. At one time it may have been a meaningless phrase but today this company mission boilerplate happens to be true. Once you got em, it' best to keep 'em. The apparent effortlessness with which people have the ability to drift from one Web site to another, as easy as pulling out a bookmark or hitting the back button on the browser, is a reality Web companies attempting to monetize their visitors and customers are acutely aware of.
Some sites are either tacitly or explicitly engaged in a lock-in play.
It's a loyalty-driving tactic worth exploring. It's a reality of information technology used to a vendor's advantage as far back as mainframes and mini-computers. When an IT user chooses a software or hardware platform they in a sense become shackled to it over time. As mission critical data is populated through the platform, as employees become accustomed to its functional conventions, as the IT organization becomes ever more knowledgeable about its complexities, it becomes increasingly difficult for the user to chuck the platform for something else since the switching costs would be so high. There is no way to avoid lock-in.