Do you have a source for this? I've heard the narrative before, but I find it slightly hard to believe there's that much value in (likely) poorly targeted ads from a system that manufacturers will probably drop backend support for in a few years.

That is not at all true. On an average, TVs have a 10% margin of the manufacturers, this tends to be way higher for newer models. If they are sold at nearly at cost, there's no point for most manufacturers to even be in the business.