Did you wantch the vid? All 4 tires were locked up in 2wd and 4wd, it should make NO difference when all 4 tires are locked

 

You're missing the point entirely. We're not talking about once they are locked up. Watch the videos again and listen to what they are saying. During threshold breaking (before lockup) you will have better braking power. In 2wd the front will want to lock up much sooner then when in 4x4. This means your stopping disctance is extended. If you can hit the brakes and not have the ABS kick in thus stopping with no drama VS touching the brakes and the ABS kicking in right away and extending your stopping distance which would you prefer? I know between October-April I do this every day when coming up to a stoplight, threshold braking to try and get the most stopping power without the ABS kicking in.

Typical 70/30 braking dynamics are not helpful on ice, 50/50 gives you much better control and traction.