How does a sorting network beat generic sorting algorithms?

In reference to fastest sort of fixed length 6 int array, I do not fully understand how this sorting network beats an algorithm like insertion sort.

Form that question, here is a comparison of the number of CPU cycles taken to complete the sort :

Linux 32 bits, gcc 4.4.1, Intel Core 2 Quad Q8300, -O2

• Insertion Sort (Daniel Stutzbach) : 1425
• Sorting Networks (Daniel Stutzbach) : 1080

The code used is as follows :

Insertion Sort (Daniel Stutzbach)

static inline void sort6_insertion_sort_v2(int *d){
    int i, j;
    for (i = 1; i < 6; i++) {
            int tmp = d[i];
            for (j = i; j >= 1 && tmp < d[j-1]; j--)
                    d[j] = d[j-1];
            d[j] = tmp;
    }
}

Sorting Networks (Daniel Stutzbach)

static inline void sort6_sorting_network_v1(int * d){
#define SWAP(x,y) if (d[y] < d[x]) { int tmp = d[x]; d[x] = d[y]; d[y] = tmp; }
    SWAP(1, 2);
    SWAP(0, 2);
    SWAP(0, 1);
    SWAP(4, 5);
    SWAP(3, 5);
    SWAP(3, 4);
    SWAP(0, 3);
    SWAP(1, 4);
    SWAP(2, 5);
    SWAP(2, 4);
    SWAP(1, 3);
    SWAP(2, 3);
#undef SWAP
}

I understand that sorting networks are really good for sorting in parallel, because some of the steps are independent of the other steps. But here we are not using the parallelization.

I expect it to be faster, as it has the advantage of knowing the exact number of elements beforehand. Where and why exactly does insertion sort make unnecessary comparisons?