I'd favour only calling the pub a brewpub when the brewery it uses is onsite, a la the Twisited. If the pub has a brewery, not on site, well, then it should be called a pub.
I still consider the Cock and Bull a type of Brew Bar. Just because the beer is brewed offsite doesn't make it any less a brew bar that Hallertau, Twisted hop, Dux DeLux etc. The main reason being that it is the only place you can get those beers.
I think the term Brewbar should be reserved for establishments that brew and sell there own beer, if they don't brew then they are just a bar. They wouldn't refer to themselves as a winerybar just because they sell wine would they?
I don't think there should be any rules. I know what a brewpub is, someone else may call it a brewbar (or a pub with a brewery). Twisted Hop is one. So is Galbraith's. Hallertau too. I'm sure there are some others but these are a few that i've visited and seen a working brewery at. I know it got up Keith's nose a little bit when Speight's set up their "ale house" around the corner. I can see why. Most people don't really care.
Isn't it false advertising though to call your establishment a brewbar when at no time is any brewing performed (unless it refers to the coffee). It would be like calling a brewery a brewbar when it doesn't have a bar.