Obstruction: Interesting

[canadaump6]

I was reading Jaksa and Roder's manual and was surprised by a couple of the interpretations on obstruction:

Obstruction on a batted ball: A fielder's "try to field" a batted ball ends immediately upon missing or deflecting the ball, and such fielder must, in effect, disappear or risk obstruction.

Obstruction on a thrown: A fielder's "try to field" a thrown ball is a similar concept to a "try to field" a batted ball excepting that a "try to field" a thrown ball includes the actual possession of the thrown ball, and the fielder's actions immediately after a miss or deflection of the ball. Therefore, a protected fielder on a thrown ball need not "disappear" after deflecting or missing a thrown ball, and if fielder-runner contact is instantaneous, there is not obstruction.

Why must a fielder disappear immediately after missing a batted ball, but not after missing a thrown ball? What is the intent and spirit of this rule? And why is this interpretation not covered in the OBR rulebook? And what happens if a fielder misses a thrown ball, lands on a sliding runner, and lies on top of him for 2 or 3 seconds? This would be obstruction correct?