For a PC, you'll most likely have USB latency, double-buffering, latency between the graphics card and the screen, latency due to picture processing in the screen. All that is additional to the 1ms that the pixels need to switch color after the instruction to do so has been received.
In addition to these excellent points, the "1 ms" pixel response time is measured grey to grey i.e. favourable to the display and not real-world. The bigger problem with advertised pixel response times is there is no industry standard measurement procedure (which grey to which grey?, is hdmi processing latency counted?), so pixel response times are vague, mostly useless marketing.
You don't have to believe these claims you know. And you need to add up all the latencies of all the components in the chain, from your keyboard and mouse to DirectX or whatever it is...