When this rule was written, the solenoid rating in watts determined the maximum current for any single operation. Duty cycle is not part of the rule. This was the solenoid used for the rule...
http://www.mcmaster.com/#69905k185/=148558h
This rule was written at a time when the GDC was putting limits on actuators as part of the engineering challenge. This part can be a good alternative for triggering latches, opening and closing small doors, etc. when a team has no other need for pneumatics.