They clarified that if you have advantage at all, then you are still considered to have advantage for anything that requires that (you just don't roll any extra dice). So a blind rogue who is invisible can still do sneak attack damage.
Oh, that's a good way to do it. I like it.
Sure, you can create ridiculous extremes of anything. The above extreme involved counting to - what - three? Even a toddler doesn't find that a challenge!
The example he posted dealt with a DM and a player counting their advantages / disadvantages in an arms race. In my 4th Edition game right now, it's the same thing, except with bonuses. And it's my least favorite part of the game.
Player 1: "I attack the orc. I have +2 for combat advantage, and I'm using my amulet to get another +3 to hit."
Player 2: "Don't forget you get a +4 because I hit him with Shield Bash last turn."
Player 1: "Right, thanks. So that's +9, plus my normal bonus."
DM: "But there's fog, so the orc has concealment, which is -2. And the orc is a blademaster, and you're in his aura, which means you take a further -2 on attack rolls. So that's only +5."
Player 1: "Alright, I activate my bracers, which negates concealment for a round..."
With advantage / disadvantage stacking, it would go something like this:
Player 1: "I attack the orc. I have advantage because I'm flanking."
DM: "Yeah, but the orc is a blademaster, anyone next to him has disadvantage."
Player 1: "Fine, normal roll then."
Less time spent trying to ferret out every bonus or penalty, more time rolling to hit the orc.