Apple has a unified operating system for smartphones and tablets (iOS), but continue having another operating system for the desktop, even if iOS features are implemented in OS X.
With Windows 8, Microsoft will have a unified operating system for tablets and the desktop. But they will be left with a separate operating system for the smartphone: Windows Phone.
No player (Microsoft, Apple, Google) will provide a single operating system that works across smartphones, tablets and desktop computers. For application developers this means web applications will be the safest bet, if you target all three types of devices. For Smalltalk this is good: Smalltalk has great web frameworks. Adoption of new UI frameworks has traditionally not been Smalltalk's biggest strength.
Apple and Microsoft will compete about the tablet market with iOS and Windows 8. But I guess the tablet market won't grow very large, and the real fight will be whether users choose to use the smartphone or their desktop computer as their main device.