Right and wrong. They do directs when they want, but you can bet that if there was some huge outcry over something and a direct could fix their public image, they would do so. Hell, there is some people that might argue they had a direct earlier this year that they did solely in response to rumors of a direct being so strong that they almost needed to have a direct or it would hurt their image if they didn't.
As for the OP. They could decide on a direct tomorrow and make it today. There isn't some insane production value in a direct that they would need weeks or months of advance prep time to make one.
I disagree Nintendo have never been phased by online reception even if they're aware of it simply because it's much better to stick to solid schedule then have knee jerk reactions that throw you off your game plan. I'd bet you they already know what they'll show in their next ND and knew before E3 even started, it's a form of guerrilla marketing and it works best in periods when things quiet down hence why January and September have often had NDs.