It is indeed an astute observation. To turn on the device one would naturally hold it in such a manner that the volume up button [on the left edge] and the power button [on the right edge] would be depressed at the same time. This then drops you into the boot loader screen. Here you are stuck if you are not a “geek” or otherwise technically adept.
The image to the left shows the boot loader screen. Looking carefully you’ll see the thumb just above the power button. The person’s first finger is on the volume up button. [That is, by the way, how you navigate in the boot loader screen.]
So turning on the Nexus S, or any other Samsung mobile device that I’ve seen [I have a Samsung Rugby], you can end up on this screen if you are not careful.
I’m not sure what you’s have to do to an iPhone t get into a similar screen, but I bet it isn’t that easy…
I don’t have that problem, not because I know better [but I do] but because my hands don’t work that way! I don’t really have opposable thumbs.