Yes, but in theory this is factored into the price. If you get 1/4 good images then a service that provided 4/4 good images could be 4x as expensive. If a service lowers their quality to push people to regenerate more often in theory those people will see their costs going up and quality go down and switch to a competitor.
This space is pretty competitive. So while tricks like this may be used in the short term to obscure the actual cost of using the service this will probably be noticed by reviewers and customers and will likely balance itself out over time.
Even if the code isn't reused adding names to sub-expressions can be very valuable. Often times I introduce new functions or variables even if they are only used once so that I can give them a descriptive name which helps the reader more quickly understand what is happening.