Apple (AAPL) executives will be taking a look at this morning's newly-published Quantcast May market share data with interest.

The figures detail mobile Web consumption by operating system across May, 2010. They confirm -- as if such confirmation were required -- that the smartphone war is between two clear leaders, Apple's iOS and Google's Android.

And Android is catching up.

In truth, Apple remains the market leader, with a huge 60 percent of mobile OS market share.

That's good for Apple, but what's less good is the 19.9 percent market share Android now holds, because it confirms just how quickly the Android market is growing.

Apple's usage figures also get an uptick from Quantcast's inclusion of traffic from iPad and iPod touch devices (also powered by the iOS) within its figures.

Is better better than best?

In terms of actual mobile Web consumption, both iOS and Android now dominate. Usage of the RIM OS and the 'Other' category remains relatively flat, with both demonstrating a historical decline.

Android is climbing rapidly, particularly across the last six months. Quantcast notes, "As we can see, in the past year Android has taken market share from all parts of the market, and noticeably so from Apple's OS."

In fact, the iPhone OS has seen usage fall 8.1 percent in the year to May 2010, while Android usage has climbed 12.2 percent.

We've seen Android grow from around 5 percent share in January 2009 to around 20 percent in May 2010.

(Note of course that these stats represent relative share within a growing market).

Apple iPhone 4

What is interesting is that Quantcast figures released last week show that, "Most of Apple's share loss has come at the expense of Motorola, who have really come from nowhere and are now closing in on BlackBerry's #2 spot," the researchers explain.

The majority of Motorola's gains are driven by Droid sales. Recent big-selling Android devices, such as the HTC Incredible and Sprint's Evo 4G will also drive market growth for Google.

What will Apple's response be?

Multiple US carriers

Some have noted AT&T's move to offer its first powerful Android-powered device, the HTC Aria, announced today. (The company has offered the Motorola Backflip before, but this hasn't lit many flames). A little lighter than the iPhone, the Aria lacks the iPhone 4's processor punch.

AT&T's move to introduce an Android-powered phone may well spark further rumors Apple will make the iPhone 4 available through other US carriers this year, with Sprint, T-Mobile and Verizon all being speculated upon as being future firms for iPhone in the US.

Diversifying carriers is one key way in which Apple can maximize market share. It has seen share gains each time it has moved to multiple carriers.

With the US market being such a large, strategically important territory, it can only be a question of time until AT&T loses exclusivity. The carrier's move to offer an Android device says this move could be on the table, as did its axing of the unlimited iPhone data deal last week.

It seems an obvious move.

Apple faces competition in the tablet market too. Android will power five different models of the AigoPad, some configurations of iPed and at least one low-cost (sub-$100) offering.

Android will also be the OS behind Samsung's future tablet, which is reportedly powered by the same processor as the iPad itself.

With netbooks powered by Android also set to ship at the end of the year, the battle for the mobile market is already at its most critical point.

To know the future, understand the past

The difficulty for Apple is that it faces an echo of the struggle for the PC in the smartphone wars.

The company's insistence on a closed system means partnership deals aren't open to it in the hardware space.

So, where Android can deliver multiple devices for multiple niches at multiple price points to the market, Apple delivers a limited number of devices, hoping the quality of its software will make a difference. It seems to attract customers that way.

As fellow blogger, Sharon Machlis, noted last week, the result of that strategy during the PC wars enabled Microsoft to seize monopoly-level market share on the desktop.

The game's not over.

Apple's share of the US smartphone market was 28% in the first quarter, according to Nielsen. Android holds just 9%, while BlackBerry has 35 percent and Windows Mobile holds 19 percent share.

Apple also holds brand loyalty, design and technological advantages others can't match. It has years of experience in user interfaces and a solid, dependable and scalable operating system (OS X) which can drive further improvements in iOS.

Software is key.

That's why Apple published this developer-focused video during WWDC, in which developers sing the praises of the company's development tools (see above).

Android Store v. App Store: Fragmentation v. efficiency

Google meanwhile has admitted to reliability issues with its online store with apps disappearing from the Android Store and developers reporting incorrect download figures and more. While Google has fixed this problem, it underlines the challenges that company has working with a large group of developers.

Despite criticism of the way it curates its store, Apple does have an App Store that works, where 95 percent of apps are approved fast.

This means developers already have a reliable and profitable route to market at 100 million iOS users - set to climb with the addition of at least 24 million more iPhone 4 users this year.

Apple's key advantage against Android is its developer community. Android developers may be able to develop more openly, but development is fragmented by the need to develop for multiple devices.

Apple developers can focus on the app.

That focus on the user experience is likely why iPhone users are so happy to remain with Apple's ecosystem, which delivers customer satisfaction levels Android can't match. One-in-five US consumers already want an iPad.

As I see it, we're at a moment of great innovation and massive change -- the meaning of which extends far beyond the evolving mobile industry, touching on the future impact and meaning of the tech industry itself.

What do you expect the outcome of this war will be?

Note: This blog first appeared on our sister site  Computerworld - read more at http://blogs.computerworld.com/evans - Email Jonny at rocket23@gmail.com.