Depends on the audience. If you're using the "Car : Vehicle" example, you're probably explaining the basics of OO to a newbie. I think that's a fine example. If you're talking about more advanced topics, then you can use a more advanced example. In fact, you can use different examples suited to different topics! Relax, there's no need to be a pedant.
Honestly, when I was a newbie, the simplistic examples drove me crazy because I didn't get the point. I can solve the toy problem effectively with concepts already introduced (functions) why am I burdening my code and my brain with all this new overhead?
The OP's suggestion to use a GUI interface is much better. GUI objects like windows are a common and interesting subject. Ironically, Object Oriented features in languages like Java and C# made a lot more sense to me after writing a Win32 gui app in straight C.
