I'm not sure I'd classify Windows as changing dramatically in its implementation, and the cost of maintaining binary backward compatibility has been considerabl

I'm not sure I'd classify Windows as changing dramatically in its implementation, and the cost of maintaining binary backward compatibility has been considerable. Only a company the size of Microsoft could afford to do it year after year. There's also a difference between building good software and building profitable or even popular software. Sometimes bad design can even help maintain a product's market lead, as if a design is complex, it's hard for competition to make compatible products. You're also still confusing abstraction and encapsulation. An API can be an abstraction over a lower-level system without being an example of encapsulation.