There arguably are no permanent sources of sustainable business advantage in any business, these days. Sooner or later, some attacker will nullify the advantage held by any single provider or firm. In a similar way, no specific business model is permanently safe from disruption.
That might be the growing case for all forms of ad-supported content, applications and services. In part, that is because use of ad blocking software is growing.
Internet access charges and user experience are the apparent drivers of such behavior. Few people claim to enjoy advertising. But an equally-big problem is the fact that advertising bumps up data plan usage. So blocking ads also reduces data consumption.
The advertising community eventually will react in a more-structured way. But stresses are growing, most especially, one might argue, in the key mobile advertising realm. Though gross revenues still are small, they are growing very fast making mobile bigger than desktop as an opportunity.