Now that I have had a chance to walk out to my truck and get my rule book, read 8.1.D, and ponder this some, I think I've changed my line of thought.
If I were to call OBS on this all the time, then this would in effect train batters to hit the catcher on their pullback every time in order to draw an OBS call. We don't want that now, do we?
In looking at the definition of OBS, and 8.1.D(4), I have to ask if F1 hindered, impeded or prevented the batter from striking at or hitting the pitched ball... (gee, just like Irish said). I could then, by rule, not have OBS (a "nothing" call).
Bah. I like learning stuff, but I hate being wrong.