The main reason, it seems, is that we watch the screen rather intently as we fast-forward so that we see when to hit “play” again. In those brief flashes we therefore still take in the more broadly stated messages.
I wonder if this will lead to a new kind of commercial with long, solid blocks of logo or key images that are guaranteed to pop while fast-forwarding. Of course, this could be completely overridden with a function that jumps you ahead in bigger chunks. Ad breaks are still very regular (either 30 secs, 1 or 2 min, etc).