They are, but only to a point. You can fail a save. You can run out of hit points. They're helpful as plot armour, but they're not guaranteed to bail you out every time.
The type of plot armour a typical novel or movie protagonist has
is guaranteed, and that's the difference: some people seem to want (or worse, expect) the game to give their PCs that same sort of guaranteed can't-fail plot armour. And if I were to go on to say exactly what I think of that some red mod-text would surely follow, so I'll just stop there....