why does isForwardRange work like this?

[Vlad Levenfeld via Digitalmars-d-learn]

I've been having trouble propagating range traits for 
range-wrapper structs.

Consider this sample code:
struct Wrapper (R)
{
        R range;

        static if (isInputRange!R)
        {
                /* input range stuff */
        }
        static if (isForwardRange!R)
        {
                auto save () inout
                {
                        return this;
                }

                static assert (isForwardRange!Wrapper); // <-- this fails
        }
}

making save @property makes it compile.

So I looked at the implementation of isForwardRange and now I am 
very confused about this condition:

is(typeof((inout int = 0)
    {
        R r1 = void;
        static assert (is(typeof(r1.save) == R));
    }));

What's the rationale behind stating the condition this way as 
opposed to, say,

is (typeof(R.init.save)) == R) || is ((typeof(R.init.save()) == R)

so that member fields as well as @property and non-@property 
methods will match, and what is the purpose of (inout int = 0)?