WingedKagouti: I've played through 20+ worlds in the course of 877 hours (according to Steam) and I've only seen one of those worlds have it's save file corrupted. And as far as I recall it that was due to me trying to edit said world with a half finished tool. Terraria save files do not get corrupted over time on their own nor do they break by being played either infrequently or constantly. That said, with as popular as Terraria has been, it's not surprising that at least some people have experienced corrupted saves without using editors.
Actually, one of my worlds got corrupted within 5 hours of playing. This was because I destroyed an altar with a life heart directly below, which destroyed half the heart and made the other half indestructible. I needed to use an external editor to fix it.
WingedKagouti: Terraria is not bug free, but something as infrequent as save files getting corrupted seems to be, I don't think it's unreasonable to say it's much harder to track down than you seem to imply. The developers may be incapable of reproducing the scenario that led to your world file getting wrecked. Your case may even be due to a couple of drivers having a once-in-a-lifetime resource conflict at the exact moment the game tries to save.
There can actually be many reasons why the save file got corrupted, even a single flipped bit could corrupt a world. Other than that, as I described earlier, the worlds can get corrupted by normal playing, but I doubt it happens frequently.