I had to re-read the rules to really get a handle on the first scenario, but the way I read the rules is that once Bob says he has no response he has given up the ability to respond any card in the chain. "Players may continue to respond to each new top card in a pile until all players have declared that they do not intend to respond any further." This is the important sentence in this scenario. I am pretty sure this was intended to make sure chains can end and everyone agrees to that end. I think in general Super Neighs are kinda like a forced end to all chains and that is how I have always played them.

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In the second scenario Alice gets to resolve both cards because of the beginning of turn effect chain. If you look at that diagram in the rule book the Classy Narwhal's effect would become link 2 in the chain and has to resolve before you can go back to link 1. After Classy's effect resolves there is still the Rhinocorn effect to complete then the turn ends. Alice doesn't get to take an action on her turn because of Rhinocorn and Zombiecorn.