Consider iCloud — Apple now offers free-of-charge online services ad-free. It’s a sunk cost in the name of the overall experience for Apple device buyers.
BS, iCloud has paid upgrades, and I imagine those paid upgrades make the rest of the model break even or better, just like DropBox. It's not ad-model vs. devices-model, it's freemium product tacked onto device sales, further enhancing margins.
Glib, but wrong.