True, that could be one way of framing the whole "using adderall/modafinil for productivity" issue. What is a "regular user" though? Someone with ADHD taking adderall in the morning to boost the "executive function" of his/her brain during the day? (as someone with ADHD, adderall sedates my hyperactive brain as opposed to its intended effect, look up the stimulant paradox for more on this) Someone who takes adderall the night before a big test to pull an all-nighter of productive studying? I've personally never heard of anyone (without ADHD) who regularly takes amphetamines to boost waking-hour productivity. Modafinil has related but different effects, regular modafinil users take it to offset the reduced mental performance brought about by sleep deprivation. There might be some nootropic effects of modafinil unrelated to its wakefulness promoting effect (cognition-wise), but like all nootropics, whether there's any actual increase in waking-hour cognitive ability is debatable.
Someone who uses a few days a week (not necessarily daily) as opposed to, say, occasional all-nighters before an exam. For example, mrleinad's comment:
> I take modafinil on a daily basis each morning, and have a regular sleep pattern of 7-8 hours a night.
It even helps with going to sleep earlier, because I feel depleted by 10 PM, so there's less incentive for me to stay up and waste time that I could use resting for the next day.