What tractor are you looking at? Generally, QAs aren't used on smaller tractors since they don't have the lift capacity to use skidsteer attachments. With the standard pin on bucket, you can still change to a set of forks or a grapple....... but they need to be made to specifically fit the dimensions of your loader arms.
Though probably not a really fair comparison........ I'll say its like having a tractor with a rear PTO, but no three point hitch. Sure, you can use a bush hog or york rake with a draw baw hitch, but having a three point hitch opens up a door to a thousand new tasks for your tractor. I'm exaggerating a little, but that is the reason QAs are so popular.