1.) PS/2 port, Wikipedia says, works at 10-16 kHz and I think protocol defines 11 bits per packet. That comes down to 16,000 / 11 = 1454.55 keys per second. True?
2.) USB default Windows polling rate is 125Hz, i.e. it has 8ms latency or lag between each packet. Now, even though each packet is 8 bytes long it seems USB keyboards still need to communicate only one key per packet, and that comes down to 125 keys per second. True?
While that may sound enough, it is only about 2 keys per frame @60fps animation, so if you play some fighter where you need to perform "DOWN+RIGHT+PUNCH" in a single frame this can be a problem, especially if there are two players both trying to report their combos in the same time.
USB keyboards are so much worse than PS/2?