First, the contact in this scenario was caused by A against a stationary B player; so no DPI (IMO).
This is supported by 7.5.10D as well as Reddings (pg 43) under PI ("players have equal territorial rights - a right to the ball"); and OPI ("Since both players (A & B, my edit) have equal rights, either player is entitled to whatever spot on the field they can get to first without contact".
The "block/charge" is an interesting analogy as it relates to a defender, prior to contact, who establishes a legal guarding position (two feet on the floor, facing his opponent if my memory serves me correctly). Both codes also allow, IMO, for the defender to move (as opposed to remain stationary) to maintain his legal guarding position.
The danger in the analogy, however, comes in that the block/charge is usually associated with a defender of the player with the ball and there is no time or distance factor required for establishment of a legal guarding position. In the FB scenario, the receiver does not, yet, possess the ball and, while the defender is allowed to move, we must be cognizant of his "cutting off", with contact, of the receiver (interfering with his opportunity to move toward, catch, or bat a legal forward pass.