The features are the same, but the 14/15 indicates where any supporting files are stored. When a solution is deployed through Central Admin, you don't have any control over this, but if you use PowerShell to deploy your solution (using the Install-SPSolution cmdlet), you can specify a "CompatibilityVersion" of 14, 15, or All (both 14 and 15). Specifying 14 will deploy solution files into the 14 hive, 15 into the 15 hive, and All into both.
SharePoint 2013 sites running in the "2010 UI Mode" will use content from the 14 hive, and sites running in the 2013 UI Mode will use content from the 15 hive. I always use the "All" parameter to maximize compatibility across site collections, but some solutions may include content that is specific to one mode or the other. This is why some of the OOB features might only be deployed to one hive or the other.