(i) That remark concerns a Bayesian agent, or more specifically an agent who updates by conditionalization. It's a property of conditionalization that no amount of evidence that an agent updates upon can change a degree of belief of 0 or 1. Intuitively, the closer a probability gets to 1, the less it will decrease in its absolute value in response to a given strength of counterevidence. 1 corresponds to the limit at which it won't decreases at all from any counterevidence.

(ii) I'm well-aware that the aims of most epistemologists and most Bayesian philosophers diverge somewhat, but there is substantial overlap even within philosophy (i.e. applying Bayesianism to norms of belief change); furthermore, Bayesianism is very much applicable (and in fact applied) to norms of belief change, your puzzles being examples of questions that wouldn't even occur to a Bayesian.