Some people are more sensitive to motion than others.
Personally I haven't had any issues with the navigation animations either, but I guess, like some people are susceptible to vertigo or acrophobia, or even sea or flight sickness, and many aren't; some people experience unpleasant feelings with the animations while many others do not.
I'd like to think Apple did not consider this could be an issue when designing the effects, and may at some point supply a way to disable the animations.
However I'm still puzzled since iOS 6 has those zoom effects except they come from the center rather than from each app icon.
The Parallax effect can be disabled in Settings->General->Accessibility.