Dead air is a very big deal in the US too. The argument is something like "licensees exist to serve the public and obviously dead air does not serve, but more importantly means that a listener might stay tuned into silence when an emergency alert is broadcast over all other stations".
It's sort of tenuous, although not wrong. Off-air is a better state than dead air.
in the 90s I remember 2-3 songs that had a couple seconds of dead-air, and the stations would modify them to play cheesy sound effects during that time. I always thought they were paranoid about someone changing the channel, but now I think it is more to be compliant.
Actually I think your first idea is more likely. I don't think the FCC would be concerned about a short gap in a song, or a pause in conversation, or a silent part of a live performance, etc.
But commercial program directors are neurotic beasts. And listeners can definitely be fickle!
One story I've heard is that PDs obsess over car listeners, who are punching "seek" (or a different preset) at the slightest provocation. They believed that a couple-second silent gap in a song would lose X listeners. They might have even had data to back it up.
I've seen song gaps trimmed, or filled with a quick station ID. Philistines!
I used to change channels like that! with terrestrial radio at least, because you can skip commercials quickly and then skip songs you don't like! Now with XM taking slightly longer to tune, (and with age) I do it less.
It's sort of tenuous, although not wrong. Off-air is a better state than dead air.