I'd be happy to provide you with a real educated answer Asraemj!
Unlike my uneducated friend Sheldor here, I refuse to tell you not to worry about it after you have already taken the time to ask. I will also not tell you Unforgiving is "pretty bad" with no comparison or explanation for my useless logic.
Sheldor's basis of implying all aspects of the game will be linear to only the first 13 playable beta levels and then projecting his/her moronic opinion upon forum viewers regarding a passive that didn't exist in the beta and respectfully, truly supports builds we don't have access to should be outcast and highly frowned upon.
Let us get started!
You no longer degenerate Fury. Instead, you gain 1 Fury every 2 seconds.
This tooltip gives zero implications that a specific situation must take place, ie. being in combat / must be out of town. Generating 1 Fury every 2 seconds should be just as simple as that, and I will expect to see my Fury bubble continue to fill while standing in a town.
Regarding a combat system, the designers tried something of the sort for swapping abilities from you action bars. This failed miserably due to D3 being a much faster passed game. Last I checked, there is no "in combat / out of combat" type system within the game. Due to the fast changing nature of the beta, there is always a possibility this have been changed once again.
As a side note, if you are tying to support a max Fury build, this passive will make your life far easier. Though, I do not feel this passive will be mandatory for max Fury builds as you could compensate with different passives and Fury generating runes.