When I first saw pinch-to-zoom I thought it was really cool, but in the long run it is one of those things that works better in "delightful" demos than in the real world.
In the real world I much prefer double-tab and two-finger tap to zoom in and out. You don't get quite the same level of "accuracy" as you do with pinch, but precise zoom is largely useless on phone/tablets anyway.
The strength of pinch-to-zoom as a UI interaction is that it is direct manipulation. It has less to do with accuracy. Two-finger tap is a "computer command" to do something. Pinch is you doing the thing you want to do.
That's a good heuristic but it doesn't trump the fact that it is physically much more difficult than double-tap or tapping zoom in/out buttons when holding a device and controlling it with the same hand which is what you want 95% of the time. Pinch zoom is definitely less usable overall.
For example, when driving nails, in theory it would be great if you could just push them into the wood but in real life a hammer turns out to be handier.
BTW, not sure about ios but in android you can turn the +/- zoom buttons back on in labs.