I think the analogy holds. The numbers in the article assume constant usage (there is a nod to the cost of static storage, but all the math is done on $3/hr gpu usage, not $0.1/mo/GB storage).

So if your usage is 4 hours per week, 50 weeks a year, you hit $600/year of gpu. If your usage is 24 hours a day, you hit $27k.

So it's not a clear-cut "buying metal is cheaper" - you have to decide how your usage amortizes. As pgeorgi says, if your demand is a pack of cookies a week, buying a bakery isn't the most cost-efficient way to satisfy that demand.