Not disable it entirely, just by default.
I've personally been rather lazy and just now got around to disabling it and clearing notifications from my email, and I imagine I'm not the only one.
This is not really a complaint per se; like I said it was my own laziness that let it go on so long - but I imagine the majority of users with it switched on don't even use the feature, and that volume of mailouts adds unnecessary load to the server.