The mine owners were not at all pleased with this arrangement, as they were well aware that they ended up paying much more than the cost of building the engine.

The mine owners were not at all pleased with this arrangement, as they were well aware that they ended up paying much more than the cost of building the engine. I believe this business model only lasted as long as Boulton and Watt could enforce their monopoly on engine construction through patents (principally on the separate condenser.) As for the 21st century, you may have noticed an enthusiasm for burdening simple products with subscriptions.