As much as new windows users don't know about ctrl+c, alt+f4, win+d... Those who don't care won't learn, those who do, will, it's as simple as that.
luluberlue
Having a mouse button being over-sensitive or being used to another middle clic behavior like windows' autoscroll toggle will tend to do that. Having a fullscreen software using MMB for something else like panning and failling to fully capture the mouse on the current screen in a multi-monitor setup also.
Like I kept surprising coworkers on windows with "witchcrafty" key combinations like ctrl+c, win+d, ctrl+s...? The middle clic paste would be roughtly as well hidden as those arcane shortcut. If users won't "discover" it, better not let them paste random stuff unknowingly at least.
Sure, if you grew with that feature and use it, it doesn't hurt you. For others though, this is pain, it fucking hurts to keep accidentally paste stuff all over due to a legacy feature.
Damn, the amount of comments that didn't even read the full... title... Is reading comprehension getting this bad? Middle clic paste isn't getting removed, just being opt-in rather than opt-out, yet a bunch of commenters are up in arms "time to ditch firefox"...
Is there a big popup at startup with windows that I somehow missed with all the shortcuts? Or did linux became sudenly less documented overnight? Why wouldn't they know? Why do you think that users magicaly knows about shortcuts almost never referenced anywhere on windows but wouldn't know about one sparking a debate among linux users with a toggle in settings directly referencing it?