Note: *In my opinion*, they're not "phoning home". Information like PHP and MySQL version is indeed being sent back as part of the core update call, but the information is necessary information to get the proper core update response. Similarly, plugin and theme api checks send information like the plugin and theme headers, in order for the api code to be able to find the right plugins and themes to check updates for.

It is perfectly reasonable for other people to see these API calls differently and say that this is "phoning home", and I can understand their point of view. For this reason, plugins exist to disable those update checks if somebody wants to do so.