Qsort Comparison Function

I am a beginner to C and I am trying to understand the comparison function needed for the qsort function.

Part One: Syntax

A simple suggested use is this (I have included some main() code to print the results as well):

#include <stdio.h>
#include <stdlib.h>

int values[] = { 40, 10, 100, 90, 20, 25, 12, 13, 10, 40 };

int compare(const void *a, const void *b)
{
    const int *ia = (const int *)a; // casting pointer types 
    const int *ib = (const int *)b;
    return *ia  - *ib; 
}

int main()
{
    int n;
    for (n=0; n<10; n++)
    {
        printf("%d ",values[n]);
    }
    printf("\n");
    qsort(values, 10, sizeof(int), compare);
    for (n=0; n<10; n++)
    {
        printf("%d ",values[n]);
    }
    printf("\n");
    system("pause");
    return 0;
}

I don't understand why you need all the extra things in the compare function so I simplified it to this:

int compare (int *a, int *b)
    {
        return *a-*b; 
    }

This still works, and produces the same results. Can anyone explain to me what I removed, and why it still works?

Part Two: Why Pointers?

Additionally, do I really need to use pointers? Why can't I just compare "a" and "b" directly like so (this does NOT work):

int compare (int a, int b)
        {
            return a-b; 
        }

For some reason, with a multidimensional array, I was able to get away with NOT using pointers and for some reason it worked! What is going on? (Example code of sorting a multidimensional array by the 2nd item in each sub array):

#include <stdio.h>
#include <stdlib.h>

int values[7][3] = { {40,55}, {10,52}, {100,8}, {90,90}, {20,91}, {25,24} };

int compare(int a[2], int b[2])
{
    return a[1] - b[1];
}

int main()
{
    int n;
    for (n=0; n<6; n++)
    {
        printf("%d,",values[n][0]);
        printf("%d ",values[n][1]);