Like Snow Leopard before it, this major upgrade will be available at a very aggressive price point of only $29, and come preinstalled on all new Macs purchased after the release. Surely Apple has poured massive amounts of cash into developing Lion -- so how can it justify selling such important software for less than the price of the keyboard?
One word: moat.
This lion eats invaders
Apple wants to immerse you in its iWorld, coaxing you into buying in (figuratively and literally) to its broad ecosystem. By letting you have Lion for next to nothing, the company strengthens its economic moat against competitors, and raises switching costs for customers in the event they ever consider defecting to Microsoft
You'll notice that Apple also doesn't charge for iOS updates for the iPhone, iPad, or iPod Touch. The company is hoping for a two-fer, and it wants all users to adopt both iOS and OS X, since this combo would maximize the odds that the consumer would buy (and preferably upgrade every year) multiple iDevices instead of a Chromebook, Android phone, or Windows PC. And if you happen to decide to load up said iDevice(s) with goods purchased through iTunes, the iOS App Store, or the Mac App store, that would just be a cherry on top for Apple.
When you add in the iCloud service, which integrates all of your digital personal effects, a low-priced Lion makes a pretty strong incentive to sit tight and make yourself comfortable. As Apple's core business is selling hardware such as computers and mobile devices, this strategy boosts sales and promotes customers' coming back for more, year after year. Apple's ability to create a sustainable, growing, and recurring revenue base is one reason investors should stick around.