Hesse notes that the iPhone is better at picking up Wi-Fi signals than Android devices are, allowing users to spend more time connecting via Wi-Fi than placing demands on Sprint's cellular data network.
He also claims that Apple's tight control over iPhone apps and its requirement that those apps meet certain network efficiency standards helps Sprint's network operate more efficiently. According to Barron's, Sprint claims that the iPhone may offer 50% more network efficiency than Android handsets.
I have no idea if it's true that Android is less WiFi friendly, but handing off stuff to WiFi doesn't really make your network more efficient - it just means your customers are using it less by using someone else's network more.
Still, if iPhones let Sprint keep offering unlimited plans for longer, and it helps them get healthier as a company, then it's a good thing.
Cheers,
Scott.