Mostly, though, it is not true lock-in, as in they mostly don't force you to do things their way. They encourage it, make the features pretty seamless to use, etc, so that you want to stay in their system, but they generally permit you to use whatever tools you want.

On an iPad/iPhone, you are not allowed to install apps not approved by Apple.

Agreed, it's the bare minimum to keep them out of trouble usually.