I've hardly ever seen people zooming with one hand (one hand on the screen, sure, but the other hand holding the phone). Maybe it works for you but, having just tried it, I find it very clumsy.
I've just looked through a load of random videos of people using their phones on youtube and I didn't see a single one where people are holding it with 3 fingers behind and two in front.
I just tried this one handed suggestion - first time ever in my 6 years using an iPhone - and I can see why I never thought of it. Extremely awkward and imprecise. I don't get why anyone would do that. Do you have giant hands?
For zooming, I've always used the double-tap method. This generally works fine for zooming in and out on Safari, and it works for zooming in on Maps. I can do a two-finger double tap on Maps to zoom out, but it's still pretty awkward so I'll keep switching to two-handed mode for those (rare) instances.
I do occasionally (meaning one hand holding, one hand doing the pinching and zooming. Not one finger from each hand doing the pinch-to-zoom). It's easier to do, and more accurate in my experience. I do pinch-to-zoom with one hand sometimes, but I find that I can't always get it right.
Ah, that's my misunderstanding. I was envisioning a finger from each hand doing the zooming. One holding + one pinching - duh, yes I do that all the time. Whoops!
