Am I using NVI?

In The C++ Programming Language 3rd ed. by Stroustrup, p.314 it explains
the use of pure virtual interfaces.

In C++ Coding Standards by Sutter & Alexandrescu it says:
Item 39: Consider making virtual functions nonpublic, and public
functions nonvirtual.

Usually I code something like this:

class Module
{
public:
    virtual ~Module() {}
    virtual void doThis() = 0;
    virtual void doThat() = 0;
};

class BasicModule : public Module
{
public:
    virtual void doThis() { /* ... */ }
    virtual void doThat() { /* ... */ }
};

class SpecialModule : public BasicModule
{
public:
    virtual void doThat() { /* ... */ }
};

NVI seems to be widely used and I just want to see if I need to abandon
my coding style for NVI.

If I consistently use BasicModule through out my application to define
the behavior, then what's the difference between my approach and NVI
except that I let subclasses override also the interface?

Thanks,
Daniel

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