What the big companies are realising is this: When you get lots of small developers using your API, you have tens of thousands of people who are actively marketing your product through your API.
You don't need to build up any large marketing force anymore, just let the developers do for you. For example, facebook connect drives people to facebook, etc. The web is becoming an OS, and the big companies are trying to achieve developer lock-in by offering a lot of convenience APIs and platforms.
It was fun to laugh at at the time, but Steve Ballmer has known this for awhile. Remember his big, sweaty "Developers! Developers! Developers! Developers!" rant?
Never forget that Microsoft is at heart a languages company. They came from writing computer languages and detoured into operating systems. Frankly, they've always been very, very good to developers.
If you're still running Windows XP, Vista, 2003, or 2008, you can download PowerShell from the Download Center or get it as a recommended update via Windows Update.
I was a Mac app startup in the days of Mac-128, OS/2 and Windows 1.0. Far from evangelizing OS/2, Microsoft sent Tandy Trower (a very important development manager, still at Microsoft) down to the Valley to visit us and urge us to develop our Mac app for Windows. He told us then that Microsoft was working on Windows versions of its Mac apps. And we were surely not the only Mac startup that Tandy had on his list of visits to make in the Valley. It has always seemed to me that developers who prioritized OS/2 over Windows were fooling themselves (easy to do, since IBM was so important then and backing OS/2), not being fooled by Microsoft.
You don't need to build up any large marketing force anymore, just let the developers do for you. For example, facebook connect drives people to facebook, etc. The web is becoming an OS, and the big companies are trying to achieve developer lock-in by offering a lot of convenience APIs and platforms.
He who gets the developers will get the users.