The "who cares" was in response to your "there's a redundant button! A redundant button!" - why is having a redundant button a big deal?
Maybe people would be confused and not understand the difference between "new multiplayer game" and "new singleplayer game", thinking they get locked in, but I believe an equal (or greater) number would be confused if there was only one "new game" with no difference between single-player and multiplayer. So I see no net benefit in removing a button.
Your alternative idea seems to be to require people to fiddle with settings in an options menu, which is supposed to be less confusing than two clearly labelled buttons conveniently placed on the main menu. I remain unconvinced by that argument.
There will be a manual which will explain these things (yes, people don't read those these days, but that's not Larian's fault).
EDIT: As I said, I don't even think the button will be redundant, as when the additional multiplayer settings are in place, there probably WILL be differences between clicking "new multiplayer game" and "new singleplayer game"
Last edited by Stabbey; 30/05/14 10:52 PM. Reason: edit