"In economics, vendor lock-in, also known as proprietary lock-in, or customer lock-in, makes a customer dependent on a vendor for products and services, unable to use another vendor without substantial switching costs. Lock-in costs which create barriers to market entry, may result in antitrust action against a monopoly." (http://en.wikipedia.org/wiki/Vendor_lock-in)
Bruce Schneier discusses lock-in: "With enough lock-in, a company can protect its market share even as it reduces customer service, raises prices, refuses to innovate and otherwise abuses its customer base. It should be no surprise that this sounds like pretty much every experience you've had with IT companies: Once the industry discovered lock-in, everyone started figuring out how to get as much of it as they can."