It's not just the accuracy, but the context switch. Apple Pay only works because you don't need to look at your phone to make it work.

their website shows people with cold weather gear

https://www.apple.com/iphone-x/

A scarf that's barely covering the bottom of the guy's face? They don't know true winter. (or, like, Muslims)

It's a tiny minority of Muslim women who cover their faces, just for the record. (I assume a head scarf wouldn't interfere.)

I'm curious: can you suggest a source for this statistic?

It's really not a controversial point. I don't know how one would get precise statistics on it, but see e.g. the Wikipedia article:

https://en.m.wikipedia.org/wiki/Niqāb

The keynote did say it works with hats, scarves, and glasses. It also works with face changes like growing out a beard.

How about a big helmet? I imagine snowboarders/alpine skiers/motorcyclist will have to take off the helmet to unlock. As someone who goes snowboarding in the winter, it sounds really annoying to not only have to remove a glove, but also the helmet, to unlock the phone (or unlock with a passcode, which is still a downgrade from using the fingerprint).

It's starting to sound a lot like:

    if (true) {
      unlock_phone();
    }