My theory and then I'm out of here before it becomes a ****storm.
The reason Japan beat us is because they are better at the game from the basics down to the advanced techniques. Because they want to excel with their character and prove themselves to be the best. They don't play for money; as it's considered gambling. They play for respect amongst their community - which means being the best player in your town, city, prefecture and being the best with that character(s). We in America, play for money. Which means after awhile when skill doesn't help us all the way, we have to resort to playing for the W in the least skillful ways possible. Whether it be through planking, timeouts or relying on the stage to carry you to victory.
Stage Choices
Alot of people scoff at their 3 stage list, because "it's not competitive enough" or it's "scrubby". The Japanese don't want anything outside of player skill to determine a victor. Sure, they may have lost on their opponent's CP but when they ran it back to their original stage, mad people got put on blast.
Adapting
The Japanese adapt so much faster than any American player I've played against. It wasn't uncommon for the to get beat game 1 and then proceed to bodybag their opponents games 2 and 3. They adapted in everything from stages to playstyles. Nietono vs Nairo in winner's went something like this: Nairo runs Olimar Match-Up.exe and wins game 1 convincingly with a 2 stock. Nietono proceeds to set-up his download process games 2 and 3. Nietono beats Nairo barely game 2. Nairo goes to Delfino (A CP stage) and proceeds to beat Nietono convincingly again with another 2 stock. They play again in loser's Nietono has him downloaded from their previous match and makes it look absolutely terrible.
Basics and ATs
The Japanese are spot on with everything as far as basics go. From shield pressure to frametraps, they have it all dialed. They learn the usefulness of each and every attack and try to utilize them. How many MKs have you seen use Dimensional Cape the way Otori and Kakera do? Their buffering is unlike anything I've ever seen. Flawless. I was watching Nairo vs Otori with Orion and I'm sure his tech skill with MK is about on par with the Japanese. He pointed out how well Otori buffered everything. Witnessing buffered Shuttle Loop OOS when Nairo SL'd his shield was more than enough for me.
The top level American players have gotten complacent with their skills. They've gotten complacent with being "good enough" to win in their region. So long as they are able to place in the money, they couldn't care less about getting better so long as they don't get worse. So maybe this was the reality check that alot of people needed to see that just because you're a "top level" player that you've still got SOMEONE (whether it be one person or 5), SOMEWHERE who is better than you and working to be better than they were the day before. Sure, this is coming from PNCATMPlayer8675 but it's the truth.