GTyankee - I checked the manual before asking. The rear view mirror section doesn't mention them, nor does it appear to be mentioned anywhere else in the manual. The video you posted doesn't mention them either.
BossHogg - Interesting idea, but I'm still wondering why they're different. Perhaps, they're intended to physically feel different so it's easier to identify the one closest to the buttons when we're not looking at the mirror. But the real buttons on the far right adjust the digital mirror, so anyone who's using the buttons is going to be looking at the mirror.