Careful with your wording, as I think you're slipping the goalposts a bit: the thing this "Open Source Maintenance Fee" is pushing back against here wasn't specifically bug reports. It was issues — a more general category, which, besides bugs, also contains feature requests. (And that, I think, is where this problem does exist "in practice.")

As you say, I don't think anyone's going to demand money to look into an (easily-replicated) bug.

A bug is, by definition, a blemish in your code quality with real-world implications; something that, even if affects no one, still feels slightly embarrassing/pride-stinging to have hanging around in your codebase. (And if the bug does affect even just one person, then it can also feel like your software is like a child or pet of yours who has accidentally done something bad to that person out of ignorance. You feel the need to re-educate your software to do better.)

In either case, you'll likely accept anything that's truly a bug into your issue tracker (rather than closing it as a WONTFIX) regardless of who submitted it, or how it got there. You might keep deprioritizing it once it's in there, but you won't close it.

But a feature request — no matter how obvious it is, or how many people want it — is different. The maintainers of a piece of code decide the direction the code evolves in; and if they never want to support some feature, that's their perogative.

Maybe you just hate the feature! Maybe it'd force the code into a less-elegant architecture! Maybe the code exists entirely to scratch your own itch, and you're not going to implement anything that isn't part of your own workflow! Doesn't really matter in the end.

It's these cases, I think, where putting money on the table would obviously sway that kind of decision. "Of all the directions you could freely choose to evolve the code... how about a little incentive to choose this one?"