You're of course right on both counts: people on Internet can be very insane.
In most circuits, fuses protect from catastrophic failures where something goes really wrong and drawing those 20A from an outlet in your kitchen, just because the panel breaker will allow it won't mean it's a bit much for an 18AWG power cord (for example).
As for Art of Electronics: it's a tad overrated book. At one time I went through the less trivial circuits and built them, one by one, paying attention to what was going on. Many didn't work as claimed, and not because of some silly mistake in the book, but because clearly nobody bothered to actually build them as described/shown.