I drew the diagrams from my perspective, holding the phone in my palm, and extending my thumb over the screen. I don't think I have particularly large or small hands. If you hold the phone further out in your fingers, you can extend your thumb farther, but the phone is less stable in your hand. The instability is where the "annoyance" comes from, when I'm using the Galaxy S II.
Do you have elf hands? I've got pretty small hands (I wear a small or medium in men's gloves depending on the brand), and with the iPhone tucked into my thumb as close as reasonably possible, I can reach every pixel on the screen, and I can reach past in spots. If I hold the phone so that it's most comfortable (and most secure feeling), I can reach way past the edge and slightly past the far corners.
Possibly more interesting is where you've put the centre of the arc, half way up the left hand side. As I hold mine, the centre would be over the bottom right corner of the screen, and at "maximum extension" my thumb is just over the top left corner. (I've got "Nash equilibrium" in the back of my head writing this... if I couldn't reach the whole screen, I'd probably change the way I hold my phone.)
