The difference is that the implicit contract is that HN is getting the keystrokes that I submit while this textbox has focus, like this text, but not when it do

The difference is that the implicit contract is that HN is getting the keystrokes that I submit while this textbox has focus, like this text, but not when it doesn't, like the entire source to the death star that I just typed out after clicking outside this textbox. The contract that you opt-into and on-by-default on W10 indicates that if I clicked the desktop and proceeded to type the entire source to the death star, there is a possibility that all or part of those keystrokes would get sent to MS and possibly stored, even though I had no intention of communicating or transmitting that information.