Good question. From the video and pics you should see that there's very little that protrudes beyond the adapter (relative to the depth of the speaker). You can also see the opening depth. The window at full roll down is still pretty high above the bottom of the door and not near the speakers. The only thing I can guess is possibly in case of water dripping from the window opening. With so little exposed, maybe it's engineered like that to keep it from dripping.
Hmmm... If someone used those Scosche's, I suggest putting them in, close the windows and then wash your car. Pull the speakers and check for water. Even if you do have water, just go get some inserts that go around your speaker and seal moisture out. They're made of closed-cell foam and you can squash them by hand.
Again, I'm 100% guessing. I know on Hondas and older GMs that come to my mind, the speaker adapters had downward facing openings. So anything dripping from above wouldn't make it's way towards the speaker assembly.
Another reason I'm speculating this is that I had washed my car (the '10 Camaro) before one of my door speaker installation sessions and there was moisture on the outside of the moisture barrier in the door.
Both my rides will smoke ya
2010 L99 2SS/RS - Hertz HE HSK 165 components/PPI A404 & A600/JL Audio 10W6/Audio Control EQX, FAST Intake Manifold