While Wintergrasp and Tol Barad both had their design challenges, always revolving around that unpredictable critter called human behavior, these World PvP Zones provided dynamics to the game you can't reproduce with queued BGs.
It was a place to play with your server mates, matching your own PvP skills against other folks from your server. While you might run across a familiar face in the regular BGs, Wintergrasp and Tol Barad were the best places to get your home server action happening. These days, Alliance vs. Horde guild rivalries feel a little silly. You don't see each other to have a real feud, unless you're on a PvP server.
The fight timing of the zones lent itself to "WoW breaks." Busy cleaning the house, studying for a test, and otherwise being a productive member of society? Well, trotting off to Wintergrasp or TB when it was up provided a nice, occasional timed break. That probably seems like a minor thing, since you could just do the same as with a BG, but the game's enforced timing gave that work-break-work habit a more natural feel. And the Pomodoro Technique of productivity is effective for a reason. This was the Wintergrasp Technique.