There is a well-known principle in Jewish law and ethics that says, "Kol Yisrael Arebim Zeh La’zeh" – "All Israel are responsible for one another." This rule was stated not only as Musar urging us to take responsibility and look out for one another, but also as a Halachic principle. It means that if one person fulfills a Misva, his obligation has not been fully met as long as there are other Jews who have not fulfilled that Misva.
This rule practically manifests itself in cases involving Misvot which can be fulfilled on behalf of another. For example, if a person hears the Shofar on Rosh Hashanah, and later he meets a Jew who has not yet heard the Shofar, he can blow the Shofar, and recite the Berachot – even "Shehehiyanu" – despite the fact that he has already fulfilled the Misva. Since there is a Jew who has yet to fulfill the Misva, one can blow the Shofar for that Jew and recite the Berachot. In theory, it is possible to recite the Berachot over the Shofar thousands of times during Rosh Hashanah – if one encounters this many Jews who need to hear the Shofar. Each time he comes across a Jew who has not fulfilled the Misva, he may blow the Shofar for that person and recite the Berachot.
This applies to Kiddush, as well. Even after one has recited or heard Kiddush on Shabbat, he may recite it again each time he comes across a Jew who needs to hear Kiddush to fulfill the Misva.
However, Hacham Ovadia Yosef, in his Hazon Ovadia – Hilchot Berachot (p. 355), writes that this rule does not apply to the case of Birkat Ha’gomel, which one must recite after enduring a dangerous situation, such as overseas travel. This Beracha, he explains, serves as an expression of gratitude and thanksgiving, which cannot be delegated. A person who is obligated to recite Birkat Ha’gomel must recite the Beracha personally, and cannot ask somebody else, who is not obligated to recite the Beracha, to fulfill this Misva on his behalf. Birkat Ha’gomel is similar in this respect to Birkot Ha’nehenin – Berachot recited over personal benefit, such as food. A person who wishes to drink some water cannot ask somebody else, who is not drinking, to recite the Beracha of "She’hakol" on his behalf. Regarding these kinds of Berachot, we do not apply the principle of "Kol Yisrael Arebim Zeh La’zeh," and one must recite the Beracha personally. This is also the ruling of Rav Shemuel Pinhasi (contemporary), in his work Ve’chol Ha’haim (p. 23; listen to audio recording for precise citation).
Summary: One who is obligated to recite Birkat Ha’gomel – such as if he returned from a trip – must recite the Berachot personally, and cannot ask somebody who is not obligated to recite the Beracha on his behalf. This is similar to the case of somebody who drinks water, for example, who cannot ask somebody who is not drinking to recite the Beracha of "She’hakol" on his behalf.
