This section is WAY too biased toward PS/2. Especially the bit about having support for a mode in one sentence and then in the next saying nobody supports it.
PS/2 or USB?
PS/2 wins on three fronts: First, it supports full n-key rollover. Second, PS/2 keyboards aren't polled, but are completely interrupt based. And third, it is impossible for it to be delayed by the USB bus being used by other devices. There are two types of USB transfer modes - the interrupt transfer mode (USB polls keyboard, when key is sensed the USB controller sends the interrupt to the CPU), and the isochronous transfer mode, which reserves a certain amount of bandwidth for the keyboard with a guaranteed latency on the bus. Unfortunately, there are absolutely no keyboards made that use the latter, because special controllers would have to be used, thus making it cost prohibitive.