It is pretty certain that not every country exercises this power, though it seems that a few other English-speaking countries also do this.

During the last quarter of century, in many hundreds of border controls through many countries of Europe and Asia, including in places with tight security like Israel, I have never seen any case of searching for information in any belongings of the travelers, like computers or smartphones or even notebooks or the like.

Israel is a country that long before 9/11 had extremely effective methods for testing travelers at border control, and unlike the Americans they kept their methods unchanged after 9/11. Unlike USA, they have never relied on technical means, like X-ray scanners or SSD/HDD searching, but they have relied on trained humans who interviewed the travelers and assessed whether they lie about their purpose or not.