I think it's a great example. It boils down to simple code that may not be obvious how it behaves within a degraded network. Your dev/QA could even have the thought and actually test it but it work under ideal circumstances giving them false confidence.

I'll go out on a limb and say it is nearly impossible to design and build a test environment that can simulate all network conditions, so that even in trivial cases where a dev might know for a fact that there is an issue, it'll be incredibly hard to reproduce it.

Maybe put another way, formal methods give cover to dev/QA to avoid shipping known but hard to prove buggy code. Bugs they will ultimately be held responsible for.