Whenever you go into options, the service process will be started if it isn't already running so that it can be asked about it's settings. If you close the options page, and none of the things the service process is responsible for were enabled, it will exit when Chrome exits. If you've enabled something that the service process is responsible for, like the Google Cloud Print connector (Options / Under the Hood, at the bottom), then the service process gets itself on the auto run list for when you log in, and will continue running when Chrome exits.
The service process will also re-add itself to the login launch list if you've enabled something it's responsible for and you then enter Chrome preferences. Because, hey, you asked it to do something, and it's just trying to do it's job.
-Scott