Apple has the iPad for content delivery. They have the iPhone for a smart phone. I hear they even make some computers. They do pretty well for themselves selling the prettiest hardware on the market and more or less controlling the gadget industry.
Google has countless tablets running Android, though their market is limited to what Amazon's Kindle Fire. Billions (unfortunately) of different Android phones exist on the market. Yes, they even have a Chrome computer that no one is buying. Still, Google is rich because their business is selling advertisements.
Microsoft has no real tablet so they made a deal with Barnes and Noble on the Nook, a device that runs Google's Android. Microsoft's only hope in the mobile market is a phone made by Nokia that critics said would be amazing if it ran Google's Android OS. Oops. Oh, and Microsoft does not really make computers since their business is selling software. Fortunately, they sell a lot of business software to offset the negative numbers from phones, Bing and Xbox (yes, they lost money recently).
Amazon is the newest kid on the gadget block with the Kindle Fire. Sure, it runs Android. Today. It seems entirely possible that they might pick up WebOS as their core for future tablets and perhaps even smart phones and computers. Why not? When your business is selling content then you can sell hardware at a loss.
The funny thing is that five years from now, who knows where we will stand. All four of these companies are making plenty of profits and Apple is clearly the leader today. Will Jeff Bezos come out swinging with new products that sell for hundreds less than the competition and kill Apple's iPad dominance? Will Google finally figure out how to build a consistent Android framework? Will Microsoft's Metro interface take the market by storm on every screen they are tossing it on? Or will Apple continue to make the greatest gadgets in the world and become the Microsoft of the next twenty years?
Grab the popcorn and Milk Duds, my friends.