The symfony configuration system uses the YAML language to be simple and readable. The ability to deal with multiple environments and to set parameters through a definition cascade offers versatility to the developer. Some of the configuration can be accessed from within the code via the sfConfig object, especially the application settings stored in the app.yml file.
Yes, symfony does have a lot of configuration files, but this approach makes it more adaptable. Remember that you don't need to bother with them unless your application requires a high level of customization.