I agree, that the snail mail comparison limps. I just included it, since you brought it up initially. Lets drop it for now.

You are arguing that simply broadcasting an analog signal fulfils delivery, even if no device is receiving it. This deviates from your initial technical limitations argument, but lets assume this is true. If broadcasting a signal without caring whether it is received or if it is, by how many devices, fulfils delivery. Then a streaming service simply needs to make their advertisement available (eg. ads.mestream.com or as clickable content on mestream.com). The ads are available for everyone and no one cares whether or how many devices access them. Most streaming services go further than that and programmatically force people to watch those ads by playing them before the main-content or by similar means.

But we know that TV stations operate differently from how you described. If no one would care if and by how many devices the signal is received, there would not be any pricing difference. But since the tech allows to know rather accurate how many devices receive a signal, a spot at 8pm is much more expensive than 3am. So we know TV stations and advertisers using TV do care about how many devices receive that signal. I would go even further and say they actually care about how many people see the advertisement. But since the technical limitation does not allow this insight, number of devices is the closest value to monitor.

I am repeating myself, but YouTube not wanting to provide services to people who neither pay a subscription or watch ads is within their rights. Whether it is a viable business strategy will show. But for you to call using an ad-block theft, that just doesn't make sense. Unless you also call it theft, to turn off your TV during commercials. If it becomes a technically and legally viable to analyse how many people are watching those ads, it would become theft to close your eyes.

Edit: changed the URLs, so they do not point to an existing service.