Though the $40 upgrade price is temporary, made me wonder just how low Microsoft will go in for future versions of Windows. For that matter, is the upgrade cycle for future versions of Windows on the brink of change?

Given the state of the competition, I wouldn't be surprised if the days of expensive, two- to three-year Windows upgrades are coming to an end.

With Windows 8, Microsoft is fighting a war on two fronts: It needs to prevent PC users from switching to Macs, and it needs Windows tablets to become worthwhile competitors to the iPad. On both fronts, Apple has been aggressive on software development, with annual updates for both iOS and Mac OS X.

A yearly cycle for major updates allows Apple to quickly respond to users' needs and add new features that help integrate both operating systems. Mountain Lion, for example, includes support for iMessages and Game Center, adds AirPlay mirroring on an Apple TV, and synchronizes iWork documents with iCloud. This fall, iOS 6 will bring Siri support to the iPad.

While iOS updates have always been free, OS X updates are getting cheaper. For anyone running OS X Snow Leopard or Lion, the upgrade to Mountain Lion costs just $20. If you're on the fence about purchasing a Mac or a PC, Apple is trying to lure you over to the Mac side by sending a message: You won't spend as much to keep your software up-to-date if you buy a Mac.