AppleInsider reports that Apple is planning to release their upcoming OS X 10.7 Lion primarily through the Mac App Store. The Mac App Store allows users to buy and install apps on their Macs running OS X 10.6 (Snow Leopard), offering a similar environment to iOS on the iPhone, iPad and iPod Touch.
Users will have the choice however to choose to purchase the physical media if they wish, but it makes sense that a full digital download is available as an option. Especially for MacBook Air users. Developers have apparently been given access to the upcoming version of OS X and we will surely get a peek at the improvements on the OS since we last saw it.
source - AppleInsider