Not so much a mistake for Sony as a mistake for Nintendo. They are the ones forced by dominance to play defense when it comes to protecting their share. Nintendo got a large bump this generation by using a new control interface to reach into untapped markets. Any reasonably good motion control system short of a knock off does present a real threat. The Move is a fairly good imitation of the Wiimote. There is a mentality among consumers that imitations are of less quality. That is good for Nintendo, but the Kinect is very different from their system. That makes it more of a direct rival.
This can only serve to deprive Nintendo of sales, and absolutely it does detract from their consoles unique qualities. The truth is Nintendo should probably have been more aggressive in acquiring lucrative patents, and locking up tech with long term contracts even if they didn't use the tech themselves. This wouldn't have stopped their rivals, but they might have been able to steer them towards more obvious copies. Perhaps even delayed them by a year. That may not seem like much, but that is time Microsoft can spend crafting a public perception that they two are a casual friendly console, and it goes without saying that extends to the brand.
This was not one of the biggest mistakes however. There is a difference between something that could have had a positive impact and something that has or is having a definitely negative impact. Missing a train is bad, but it is by far a worse fate to be hit by a train. Gaming is full of train wrecks. Horrible format choices, poor quality assurance, poor security, Consoles that do not last a year, peripherals that don't even last that long. Carts over discs, Molten 360s, The PSN Hack, The Virtual Boy, Super Scope, and Power Glove. All of that after the entire console market crashed. Hell I hear there is a pit out in the desert filled with E.T. Games. This just isn't even a bump in the gaming landscape. There are far more horrific tales.
