For all the focus on digital media, television is still the powertrain of the advertising economy, and nothing shapes perceptions about the underlying strength of the US advertising economy like the upfront television marketplace.

Last Spring's upfront saw advertising commitments on the major US broadcast networks grow at double-digit rates, fuelled by a relatively tight supply of advertising inventory and perceived pent-up demand from advertisers.

That would be true if the upfront was a genuine ‘leading indicator’ of advertising demand. And while Wall Street analysts and publicly traded television companies have...