What they're getting at is that the latency is caused by overhead from the OS and USB, increasing it across the board regardless of editor — each keystroke has

What they're getting at is that the latency is caused by overhead from the OS and USB, increasing it across the board regardless of editor — each keystroke has more layers to pass through compared to a machine from the 70s, 80s, or 90s, plus USB by the nature of how it works unavoidably adds latency that's variable depending on CPU load, since USB is CPU-dependent. There's also more layers in the display stack, increasing the amount of time it takes for what's actually displayed on screen to match machine state. A Core 2 Duo era laptop specifically might not suffer as much as its desktop counterpart though, because laptops from that era often used PS/2 for their internal keyboard+trackpad connection and thus don't suffer USB latency increases unless the laptop's motherboard was doing something weird like implementing PS/2 via an onboard adapter attached to the USB bus.