Assuming a good cash-back rate of 2%, $2000 spent on the credit card for $40 back.

The point being he's spending the $2000 anyway, so he'd rather get $40 back from his credit card company rather than $0 back if he used cash or debit.

But cash-back is not the same as reward points.

Cash-back is "money", reward points (more or less) is "discount on given good".

Many cards let you cash out rewards points now. With Chase, for example, you can get a check in the mail, use points to pay off your CC balance directly, or use points on amazon (at full value).

Using Chase Ultimate Rewards points at Amazon is only worth 0.8 cents per point, not 1 cent per point like the others.