And often it boils down to an intangible "we felt a better vibe with candidate B" and that's probably something they will never come out and say.

My reaction to the feedback he got when he finally jogged someone into responding was like yours. It was the typical cliche rejection letter. Maybe a bit more personal than some. I'm sure that the "wires got crossed" and the "email never made it to your inbox" are just a smokescreen for "we hired someone else and didn't bother to let you know."