Nick, in your last example, if the two calls went by pretty quickly, I'd honestly probably give the player the benefit of the doubt and give him a warning and his second card despite there being substantial action, strictly speaking. I'm not that unreasonable...
But in the original post, there was a "lot more" significant action if you will, so much so that I cannot accept that there was any valid excuse for delaying bringing the allegedly missed card to the dealer's attention. If the button is not dealt the last card in error, he is entitled to it... but this "right" cannot last forever IMO. If so much time has gone by that
the dealer can no longer be reasonably sure that he did in fact miss the button (I think that is really the principle that should govern), then we have potential game security issues; in those situations, I'd rather the sequence of unseen board cards be off, then allow for the possibility that one player may have been given a second chance to be dealt a better hand (or to give other players remaining in the hand that perception).
I also have heard players point out that they do not act on their hands until it is their turn. This doesn't persuade me. You don't have to look at your cards if you don't want to, but you really don't have to look at your cards to simply determine that you were dealt two.
I think what you are saying is that if we assume in the original question that we are 100% sure the button did not receive the last card, he should receive it. I would not fault any TD who wants to make an exception and give that last card. However, in most cases, if a lot of time has passed and/or a lot of action has occurred (and when substantial action has occurred, this will probably the case most of the time), I would suggest that you simply cannot be 100% sure.