I second thehostinglist. For most customers, just get a web site up and running is more magic and guesswork than anything else. Once they're running somewhere, they don't want to go through the hassle of switching.
You'll find many people are tolerant to problems and downtime if given an adequate response.
But, there are different kinds of customers... technical ones will always look for the most control, bargain hunters with some knowledge will always go for a better deal, and the less technical will move if they find a more personal experience. I think the vast majority are scared of the idea of trying to move a site.
Most people aren't used to the basic ideas of computers (eg what a windows is, what the window is doing [settings, logging in, informing them, spyware etc ]) so having to combine the lack of knowledge of computers (and even getting to something like a control panel or FTP program) with the added complexity of using the tool appropriately is a truly daunting task.
Perhaps it's because they are happy with their current provider. Think about it from the client's perspective: you're happy with your current hosting service. You may sometimes think you're paying too much, but if you have no other complaints, why switch to a provider you know nothing about?
In other words, don't fix what ain't broke!!
Daniel B., CEO - Bezoka.com and Ungigs.com Hosting Solutions Optimized for: WordPress • Joomla • OpenCart • Moodle Data Centers in: Chicago (US), London (UK), Sydney (AU), Sofia (BG), Pori (FI) Email Daniel directly: ceo [at] bezoka.com
It's also because of loyalty. If a customer is with a host long enough, they tend not to switch even though there may be reasons to, simply because they are loyal to that brand. Take 1&1: They offered 3 years of free hosting, and many of those clients returned to a paying package afterwards.