Last week Apple announced that since July 2008 more than 10 billion iPhone & iPad apps have now been downloaded from the App Store. For those counting at home, that an average of 18 million apps per day.

Despite the significant head-start, today Google announced their own Web-based store app store called Android Market, which is designed for people to get to new applications for their Android-based smart-phones and tablets.

Up until now, those using smart-phones based on the Google Android operating system were limited to discovering new apps only from their devices, while users of Apple-based devices could search for new apps using the popular iTunes software. Now Android owners will be able to discover and buy apps from any Web browser, which will automatically sync to their devices.

Google and Apple have very different strategies with respect building to their app stores. Apple’s game-plan has been a tightly-controlled system in which developers need to pass strict requirements to be listed in the store. On the other hand, Google doesn’t have an approval system, so developers can quickly submit and revise their applications at will. Apple’s walled-garden approach has long been one of the biggest complaints for app developers, limiting what they could release and sell based on Apple’s ever-changing restrictions.

Another fundamental difference between the two is that the Android OS is open source and the technology is designed to be extended by an active community. The open source approach has been proven to drive faster innovation and wider adoption in countless examples and Google is counting on it to best their proprietary competition.

One other significant advantage of Android Market apps is that they do not differentiate between the phone’s core applications and one’s developed by a third-party. This means developers have equal access to all the mobile device capabilities, providing users with a broader spectrum of available services.

Importantly, both companies do allowing developers to sell inside of apps. However, all payments made through the iOS generate a 30% cut for Apple, while Android developers receive 70% of the app price, with the remaining 30% distributed between carriers and payment processors.

So, will Google Android Market catch up with Apple’s App Store?

While the iPhone 4 was the best-selling mobile phone in the US during the fourth quarter of 2010 with access to over 350,000 apps, the Android OS is hot on its heals running 53% of all US smart-phones, including the Motorola’s Droid X & Droid 2 and HTC’s Evo 4G, with access to over 130,000 apps.

Google and Apple are positioning themselves with fundamental different strategies, but in the end it’s another classic proprietary vs. open source battle. Will Apple proprietary devices just become another beloved relic and the mark of an era?

Only time will tell as the race to the first 100 billion apps is now on between Google’s Android Market and Apple’s App Store.