You sir, beat me to it. Amazon Whispernet is what it's called, and it's exactly the right argument to make here. I was actually having a conversation with some coworkers the other day about something similar.
Amazon made a deal with one or more national cellular carriers to be able to deliver purchased books to user's Kindles. When Amazon pushes a book, I imagine they pay whatever carrier they used to deliver it a nickel or something. So figure an automotive update is what, maybe 2 GB? I can buy a 3 GB data plan from AT&T or Verizon for $30, so let's call the data rate $10/GB (and that's high because it's the consumer rate, auto manufacturers would quite positively get some sort of discount due to their buying power). So let's say it would cost the automaker $20 per car to push the update OTA. Now compare that with what they have to pay the dealership in labor to do the same update. Last time I checked dealer labor rates were something like $70/hr with an hour minimum. This saves them 71% on their costs to have the updates rolled out. So lets say Ford sells 50k F150s a year. If they have to push an update to all 50k of them, assuming the dealer update cost is $70 and the OTA cost is $20 then the dealer update cost is $3.5 million, OTA cost only $1 million. Savings of $2.5 million per update.