You must have come around many hosts offering "free migration services".
Web hosting companies, who have a good client base and signup ratio is high and offer this services would get benefited of this. You may ask how? Your technical support team whether it is an in-house team or an outsourced web hosting support company who are already busy with clients solving their technical support issues cannot concentrate on migration due to their daily routine work load which is already high. In this case, we take over and handle "website data migration" for your new clients who signup with you. Mid-size and upcoming hosting companies can also offer this "website data migration" services and can increase your client base.
We have a specialized team who are experienced in website data migration - we have experience in migrating data of domains from any web hosting control panel. If your hosting clients have any CMS like Joomla, Mambo etc... or blog like WordPress we know where should we set the databases in your configuration files which makes migration easier.