Farmer - I think I get the jist of what you are asking. You want to know why someone would call for LVL change after having selected N1 during the climb out because according to your understanding of the AFDS, You can simply just wind up the speed and it will follow the speed anyway (without pressing LVL change).
according the this FCOM VOL 2 - in auto flt section, it says
that after the aircraft is airborne the FD commands 15deg pitch until a predetermined ROC is reached then it commands MCP plus 20kts (ie V2 plus 20)
So by just winding the speed selector up at your acceleration altittude and not selecting LVL CHG the aircraft will accelerate to the new MCP SPD PLUS 20kts (ie the pitch mode of the FD will still remain in TO MODE).
This is overcome by selecting a new pitch mode. eg. LVL CHG which will force it to follow the actual MCP speed. VNAV is not selected until flap retraction due to possibility of flap overspeed issues.
btw by selecting LVL CHG at 1000 and not N1 the aircraft will fly V2 speed and if there is less than 2.5 mins since takeoff then engine will remain at TO thrust.