As is usually the case with major application releases, there is both addition and subtraction. Some features of SharePoint 2010 (pictured) have been removed in 2013, or will be in a future release. These include things such as certain site templates, Web services, and other under-the-hood elements. Microsoft notes that many of the retired features are related to the significant changes to search functionality. The company has published a full list, along with notes, at the Technet site. We recommend you read it prior to kicking off an upgrade.