Apple were already using USB for the PPC iBooks, and continued that with the Macbook - Linux has always complained that it can't find a PS/2 controller on x86 A

Apple were already using USB for the PPC iBooks, and continued that with the Macbook - Linux has always complained that it can't find a PS/2 controller on x86 Apples. But USB is poor from a power management perspective, and so input devices on low power systems are frequently run over SPI instead. Apple began this with the Macbook (which is basically a tablet shaped like a laptop) and have started extending it across their entire mobile range. There are entirely sound reasons for doing this, and it's not unique to Apple.