What about watching Netflix and iTunes?????
Your eyes natural field of vision is "widescreen" so how can narrow-screen vertical make sense (other than Face Time/Skype)? The iPhone in landscape more closely matches your natural field of vision.
Also the purpose of this thread is about all of the "important" events captured incorrectly (wrong aspect ratio and vital information missing) for posterity and shown on YouTube and TV/cable news type shows. Maybe you would understand the correct from if shooting something important but the majority of people don't. We need to be protected from them in some way like default Landscape video (you can still select vertical if you want).
Another advantage to default landscape video recording. It much easer and more stable holding the iPhone in portrait to shoot, plus you can do it with 1 hand.
I doubt as many people watch Netflix or movies on their phone vs those who watch short youtube/facebook clips. Plus it is easier to hold your phone vertically. I am with you tho, I cannot stand vertical videos but I am not going to tell others how to do something...
We could just change the industry to have all screens square so it won't matter which way you're holding it