I'd like to add my perspective
on this notion as well, I guess. Being an arcade gamer, I'll point out that I garnered this technique from and while playing against young black kids, rather than asians. But it's not just double finger tapping, it's using every finger on your hand
that you can. I've found that the people I've played against who were the best at breaking out with vicious combinations of shorts to fierce fireball two-in-ones
were the people who were using three or four fingers.
I played with mostly my index finger when I was a bit smaller, when first learning how badly schooled I could get at Mortal Kombat. When playing MK3, I was up to using the index and middle fingers for sequencing purposes (chain button combos). My technique had improved immensely, but then I finally got into the Street Fighter genre with a serious attempt. The first thing to do when learning a new game is to play it's console counterparts at home with your friends. If you want to play the newest version at the arcade, there's a chance (i.e. it's damn near impossible that this won't be the case) that a character from an older game will be in this sequel, and he'll have the same basic repertoire of moves. Also, there will likely be other characters with the same inputs for similar moves. I had played Street Fighter before though, and while I played Blanka when SF2 first came out, I wanted to play a more technical character, one with better defenses and good zoning ability (the ability to push your opponent where you want them to be, usually the corner). I, like the goon I am, chose Ryu (note: everybody chooses fuckin' Ryu). Well, it wasn't but a few years later that the character of Evil Ryu came about. He has a raging demon combo like Akuma, and I'm gonna have to say, if you can surprise your opponent, and put this move on them, you will seriously ruin their odds at beating you during the current round.
Anyway, home gaming is one thing, you can fix the buttons on your controller so that you can jam on them all with your thumb. Raging demon? No problem. At the arcade however, I found myself failing to do this move more often than not; it made me look like a 'tard, and left me open to attack. You see, the button pattern is jab, jab, forward (on your control stick, not the middle kick button), short, fierce. This pattern caused me to tangle my fingers when I went for the short kick with my middle finger (it's right below the jab button, and the next finger movement is to the far upper right, so I'd have had to tap the first three with my index, and then go for the reach with my middle finger, but I accidentaly made the third push with my middle finger a habit). So... I brought in my thumb, giving me a final tally of three digits, which is what I've been up to in my current stay at the arcade machines.
Basically, the point is this, single finger tapping doesn't get a lot done for ya. Double tapping is better, and if you can add more fingers from there, it can only help you out.