Windows laptops often apply PS/2 for built-in keyboards and pointing devices (mice, touchpads, trackballs).

As the manufacturers of the built-in devices are different from the chip set vendors, some standard for the connection have still great benefit for both sides, upon circuit design, communication protocol, production and cost.

As PS/2 has been established on external keyboards / pointing devices, they didn't hesitate to apply PS/2 directly for the built-in devices. At this point, the total cost of PS/2 was much less than newly designed I2C device. Recently USB becomes established for these devices and the cost is gradually lowered. Then, built-in USB devices will increase.

Tsuneo