If you look at how regular people are using phones and installing application on Android/iOS and WP, that is very similar to how Windows users install and use software (trusting a lot of application from a very wide variety of places)
But on windows you have anti-mall-ware and anti-virus software protection and on mobile you have limited rights because of sandboxing.

That is very different from how users should install applications on any Linux desktop. If Ubuntu Phone is supposed to be used by the same customers as iOS/Android, it should use security features like sandboxing by default.
Without proper education/warnings people shouldn't be able to install applications that can steal your data or use phone hardware without the user's knowledge.