Not everyone looks like the dudes in a porn. Don't you think the camera man or someone else there wants to jump in? They are probably like most guys and closer to average. Which I think one of the more recent studies says is about 5.5" I believe.
But in my experience, most girls don't like to be bottomed out in as it pushes on cervix and uterus. Many girls don't normally get off from normal sex. But if they do it's normally because you stimulate the g-spot. If you want directions to it let us know. But it's only about 2" inside so you don't need to be super man to hit it. Different positions help stimulate it as well as practice and knowing where it's at. Then you can use the, err, head to rub back and forth increasing friction. A lot of pleasing girls is wanting to, and learning your way around.
But some girls just don't get much from actual sex. It's the foreplay and going out to eat where they get theirs. But once they have one they are much more likely to have another. A tip, if you feel they are having an O, most get extra sensitive. So don't keep going at it out you might get pushed away. Instead stop, and make very small movements and they many times will keep going. When it stops start back and many times they hand another. Lather, rinse, repeat. It's amazing how many and how long can keep it going. It must be much more intense than us guys little bottle rocket with a fast report at the end. Also, the vibrating rings they sell next to condoms help. This stimulates the outside while you are going for the inside. It's really great when you both meet up on time.
It can be intimidating at first but if they get theirs first then you don't feel too bad when your the 1 minute man. To me, getting the girl off is half the fun!
Hopefully this isn't too much detail here!