The iPhone OS has changed its name, and when it's released for the iPhone and iPod touch this June 21 (free), it will be juiced with expanded money-making opportunities for developers.

Today, at his Worldwide Developers Conference keynote, Steve Jobs let his 5,000-or-so most ardent admirers know that iPhone OS 4.0, announced on April 8, is now iOS 4. Which only makes sense. Having started out merely on the iPhone, Apple's mobile operating system has spread to the iPod touch and the iPad — and the name iPhone/Pod/Pad OS 4 doesn't exactly roll of the tongue.

Jobs gave an overview of iOS 4's capabilities, adding little new beyond that which he unveiled at the iPhone OS 4.0 announcement: multitasking, folders, improved data protection, device management, wireless app distribution, support for multiple Exchange accounts, a unified Mail inbox, SSL VPN support, Exchange Server 2010 support, and the like. He also pointed out that iOS 4 will include 1500 new APIs, including such niceties as in-app SMS and performance-profiling tools.

What appeared to best float Jobs' boat, however, was the upcoming launch of Apple's iAd mobile advertising platform, which is scheduled to go live on July 1. Jobs said Cupertino has so far received $60m in commitments from advertisers for the remainder of the year.

But why is Apple launching iAds? "To help our developers earn money." Or as his presentation slide explained a bit more fully: "To help our developers earn money so they continue to create free and low-cost apps." Which, of course, sells iOS devices: iPhones, iPod touches, and iPads.

Remember, Apple has admitted that its App Store is not a money-maker — its 225,000 apps are there to entice purchases of hardware. And that enticement is working: Jobs claimed that the 100 millionth iOS device will be sold this month, and that last week the number of total App Store downloads passed five billion.

Apple has never revealed how many of those downloads are free apps and how many are paid. Frankly, it doesn't care, other than it wants to ensure that the devs who are cranking them out keep cranking them out. And to ensure that they will, Cupertino needs to make doing so worth their while.

The iAd equation is that developers will get 60 per cent of the ad take. As Jobs told the devs in today's crowd, Apple will sell and host the ads, so "all you have to do is tell us where to put them, and then make money."

And when devs make money, they develop a deep affection for the platform that pays them — and Jobs noted today that Apple has passed $1bn in App Store revenues to devs. So far. The Apple ecosystem in which developers create the apps that drive iOS devices sales will only get stronger when iOS 4 is released this summer for the iPhone and iPod touch, and this fall for the iPad.

Steve Jobs isn't rewarding devs for their loyalty or painting over the vagaries and inconsistencies of the App Store police with bucks. He's merely emulating the wisdom of "Monkey Boy" Steve Ballmer when he famously chanted: " Developers! Developers! Developers!" Developers! ®