It's a fairly arbitrarily number sure, but I think it could be representative. During the working week I listen to music almost all the working day, when I as commuting that adds on another couple of hours.
Even if it's 2 hours a day it would still represent an increase in costs.
Another poster put it better: for $9.99 per month you would be able to pay for 999 streams, I am sure a typical user can easily exceed 999 streams in a month.
Well for instance, I'm on a family plan (6 people total for $15) and I stream a full workday+ daily. I know lots of people who do the same, where they have a lot of "background music" time and then a little active listening.
Even if it's 2 hours a day it would still represent an increase in costs.
Another poster put it better: for $9.99 per month you would be able to pay for 999 streams, I am sure a typical user can easily exceed 999 streams in a month.