By the definition, software isn't an economy of scale. Unit cost doesn't decrease by magnitude as output increases. A utility company is an example of economy of scale.
Economies of scale don’t just have to be areas where unit marginal costs decrease as volume increases, they can also be areas where fixed costs dominate marginal costs, which is the case for many software firms because marginal costs are usually very small
Economies of scale exist when the average cost decreases as the number of units increases. The average cost for N units is the sum total of all fixed and per-unit costs divided by N.
