It guarantees upto 40 degrees of bank. (1.4g) It also includes a 20kt buffer to the amber band. This is to protect against those not monitoring the flap gauge and slowing to a lower F number without the flaps having moved; thus being 20kts below the F number.
RAT5, my assertion is same as yours except I have never heard about the 20 kts buffer?
Flying min maneuvering speed during moderate turbulence, in a turn, combined with inattentive pilots, could take you uncomfortably close to stick shaker and most likely induce some hair rising AIRSPEED LOW alerts.
As we are on the topic of maneuver limits. Look in the FCTM and check the maneuver margin as you raise Flaps 1 to Flaps Up. The LE devices are retracting. If it wasn't for the requirement to have positive acceleration towards Up-speed, and the slow retraction of the LE slats, it would actually take you into the amber band. As this often coincides with a turn as part of the SID, the Pitch Limit Indicators are not that far away!!