It is insteresting and instructive to take a step back from the big ecosystem builders and think about who their customers are and what they are selling. Just so we all start from the same point on the map, I am going to clarify that customers are the people that pay and they pay for whatever a vendor is selling.
Microsoft
This is a big week for Microsoft with the long anticipated Windows 8 launch. Even though I am very much looking forward to getting my MS Surface (hardware) this week, Microsoft is still the maker of software and its customers paid $16 B in the most recent quarter and generated $5.3B in profits including for operating system software ($3.2B revenue /$1.6B profit), servers and dev tools ($4.5B/$1.7B), and productivity and business software ($5.5B/$3.6B). This is highly profitable business with one half of all revenue returned in profits. You will notice that a bit over $2B is missing from this revenue analysis - because that is the amount MS generates from XBox -- without generating any profit. Ouch!
Simply, customers pay Microsoft for the software they need to be productive. Anyone who has tried to be productive on an iPad knows what I am talking about. Producers need Microsoft's products to produce.
Apple
Apple quite famously makes more revenue and profit on the iPhone than all of Microsoft combined. In its most recent quarter it generated $16.2 B of a total of $35B from the iPhone at 43% margins. Any company that can grow from zero in 2007 when the iPhone was introduced to over $60B in annual revenue from a single new product line - deserves to be the worlds most valuable company. Even more impressive is the $9.2B in iPad revenue last quarter from a product just 30 months in the market. However, as Apple is demonstrating with the change of the standard cable plug on the latest version of the iPhone - it is selling devices that are driven by their popularity, not by business acceptance.
So, customers pay Apple for fashionable gadgets and Apple cranks out fashionable gadgets like no one else.
Google has revenues about the same size as Microsoft's. The most recent quarter concluded with $14.1B in revenue and $7.45B in profits. 75% of Google's revenue comes from advertising. Advertising was 97% before the acquisition of Motorola -- and Motorola now makes up 19% of Google's revenue. Google makes all kinds of software (gmail, Google docs...) but most users get those services for free -- and the customers are the companies that pay to place their advertisements where those users can see them.
So customers pay Google for advertising. Google dominates the search market with 65% of all internet search traffic.
When analyzed from the perspective of the paying customer it is almost hard to believe that these three companies are fierce competitors. No one buys Microsoft products to be seen with them in the first class lounge at the airport. Almost no one pays Microsoft for advertising. Just about everyone pays Microsoft to make their businesses run.