I initially thought this too, until reading the content of that point. The emphasis is really predictability in this section, even if usage is consistent, customers will have a hard time trusting it if they don't understand what it is based on.

Cloud providers are generlaly selling to technical customers. But you need to make sure you pick metrics that your customers understand. If you were selling a recipe system and your target market is restaurants and chefs, would you charge for PostgreSQL table usage or the number of recipes that can be stored?

Saying you can store 100MB of table data, but that should fit for your 100 recipes, is different than directly specifying that your plan includes 100 recipes. Even if the customer plans on never actually having more than 80 recipes.