I want to take a break from the deafening speculation about Nokia’s announcement tomorrow and instead direct your attention to this solid piece from TechCrunch examining the struggles of Apple’s iAd business. Fill rates for the mobile ad business have dropped dramatically in the last several weeks, according to writer Erick Schonfeld, while some competing ad networks seem to be thriving. Schonfeld cites a number of factors including iAd’s step pricing, a lack of visibility into ad placements and the fact that the ads run only on Apple devices. I think Apple’s insistence on playing a role in the creation of ad campaigns continues to be a drag as well. Add them all up and it’s clear that iAd continues to fall short of Steve Jobs’ expectations, as I predicted last June.