There's nothing wrong with comparing the business model of one company to another & scaling it up. There are plenty of industries out there where the initial investment is breakeven or small profit but the support / accessories make most of the profit.
If Coffee machines don't suit you, car sales is a much bigger ticket item & work the same way for dealers. The Ford dealer doesn't make much selling you a Ford Focus but he makes a lot with the services & accessories that go with it (floor mats, oil changes, warranty work, etc.)
The main reason I compared it to a Keurig is because it's basically the same premise, its an easier / more convenient way to do something. A Blademaster or Blackstone machine with a competent sharpener can do a better job than a Sparx with the flexibility of doing any hollow you want when you want but the Sparx will let any Joe Schoe sharpen their skates at home that's good enough for a majority of people & all they need to do is buy Rings (K-cups) after X amount of sharpeners & that's it