Good point on the top bar. I still have a YouTube account that I'm almost positive wouldn't log me in to anything besides YouTube, maybe that's not true or maybe its just because I'm grandfathered in.
You can still avoid it if you really want to. My account is now a google account but my flatmates youtube account is still separate. They keep bugging him but he keeps dodging it, wont agree to the new terms.
I would guess there is a limit to how long he will be able to dodge. At some point there will only be an agree button.