It's the same for the host controller hardware, it exposes different interrupts which the host controller driver can make use of so you don't have to busy-wait. The details depend on the host controller interface the hardware provides though.
The polling by the host controller is still limited to happening once every bInterval period as specified by the device, which for mouse/keyboard will be at least a few milliseconds, v.s. the old school PS2 style mice which would send hardware interrupts straight to the processor.