[0]: http://googleplusplatform.blogspot.co.uk/2013/02/google-plus...
[0]: http://googleplusplatform.blogspot.co.uk/2013/02/google-plus...
create a new account. agree to gplus. comment on youtube or use hangouts on device X. pronto, it was so frictionless that you didn't even notice. not it is public that you are using device X and that you commented on some youtube video.
what you say may be true for non-google services, which twitch does not fall under anymore.
Where are you seeing which device you are using shared on Google+? The only place I've seen something like that is if you have someone you've accepted as a Hangouts chat buddy and you've opted into the "share which device I'm on" in the Hangouts settings (all that shows though is if you're on a tablet, phone, or desktop computer though, not specifically which device).
1. how long my mentioned comment on you tube (for example) is tied to gplus
2. when that checkbox was added.
you will surely see its at least a six month difference or more. now some doesnt even have that option yet... but hopefully you will get the point with just example