As I see it, the ultimate goal of drivetrain maintenance in long-distance cycling is to avoid replacing any of the chainrings (i.e. the gears on the front): while you might be able to replace your chain yourself anywhere you can have parts shipped to you, and you'd probably be able to replace your cogs in any town large enough to have a bike shop at all, replacing any of the chainrings would probably involve that part being shipped to a bike shop in the town you're in. Plus, they're more expensive than cogs.
I'm pretty sure if I'd started this trip with a fresh set of cogs and a fresh chain, that I could have gone the entire route to DC on the same set of cogs provided I had chain replacements every thousand miles.
None of that having been the case, what you see here is a fresh set of cogs and a fresh chain.