Why the basic example of service in ROS2 doesnt use rosidl?

edit

I am not sure if this is it, but in the ROS2 tutorials the package example_interfaces is used - there in CMakeLists.txt you have these lines:

find_package(ament_cmake REQUIRED)
find_package(rosidl_default_generators REQUIRED)

rosidl_generate_interfaces(${PROJECT_NAME}
  "action/Fibonacci.action"
  ...
  "srv/Trigger.srv"
)
install(FILES mapping_rules.yaml DESTINATION share/${PROJECT_NAME})

ament_export_dependencies(rosidl_default_runtime)
ament_package()

and in package.xml:

<package format="3">
  <name>example_interfaces</name>
  <version>0.9.3</version>
  <description>Contains message and service definitions used by the examples.</description>
  <maintainer email="mabel@openrobotics.org">Mabel Zhang</maintainer>
  <license>Apache License 2.0</license>
  <author email="dthomas@openrobotics.org">Dirk Thomas</author>
  <author email="jacob@openrobotics.org">Jacob Perron</author>
  <buildtool_depend>ament_cmake</buildtool_depend>
  <buildtool_depend>rosidl_default_generators</buildtool_depend>
  <depend>action_msgs</depend>
  <exec_depend>rosidl_default_runtime</exec_depend>
  <member_of_group>rosidl_interface_packages</member_of_group>

A note about package_name_interfacesfrom https://docs.ros.org/en/foxy/Tutorial... :

While best practice is to declare interfaces in dedicated interface packages, sometimes it can be convenient to declare, create and use an interface all in one package.

The dependencies in the basic service examples are fulfilled with ament_target_dependencies(service_main rclcpp example_interfaces) in their CMakeLists.txt(e.g. https://github.com/ros2/examples/blob...).