I think the discrepancy is an error. Note that at the bottom of the description of how the Adrenal Moves work in RM2 Character and Campaign Law (red band edition, p. 53), there is the note, 'Note: Use Presence stat bonus for all Adrenal Moves'. This is there despite the fact that there is no stat bonus mentioned in any of the skill descriptions above this note. We always took that to mean that the stat bonus was intended to be added to the rolls, even though the verbal description spoke only of 'skill rank bonus'.
RM Companion II also listed 'PR/SD' as the stats for Adrenal Moves, so it would be odd if these stats never came into play.
Fun fact: the original Character Law (RM1, or First Edition, p. 12) said, 'then adds the bonus for his skill level in Strength Adrenal Move'. So I think the error might have crept in during the move from first to second edition, or from the first printings of second edition to the red band printing.
Further confirming this impression, the first edition printing of Character Law (p. 12), in describing Adrenal Balance, reads, 'skill bonus'. Though this is in reference to the bonus that applies after the concentration maneuver has been made, it does read 'skill bonus' in RM1, but that has been changed in RM2 (red band) to read 'skill rank bonus'. So a change has clearly been made, and I really think it must have been done inadvertently.
Finally, both RM1 and RM2 had the chart that listed PR (and PR/SD if using the optional rule about multiple stat bonuses) as the stat for Adrenal Moves.
Final Note: The rules for maintaining adrenals in Companion IV do clearly read 'skill bonus' rather than 'skill rank bonus', at least for the roll to maintain the adrenals.