It is true that no Catholic is bound to believe in apparitions. However, it goes a bit beyond just "approving the message" of an apparition. For example, Our Lady of Guadalupe has basically no message for anyone. The apparition and the miraculous tilma is the message. The Church has made Our Lady of Guadalupe an official feast on the universal liturgical calendar. She has been proclaimed patroness of all the Americas by Pius XII. Her feast is a holy day of obligation in Mexico. It's everything short of "believe this as revealed dogma". 

Medjugorje: questionable. Fatima, not exactly. Again, we have numerous popes attempting to follow the actual requests of Mary of Fatima (consecration to Russia for example). We have the CDF actually revealing and explaining the 3rd secret in official act of the Holy See in year 2000. Every pope since 1917, including Francis, has liturgically celebrated May 13 and/or October 13. Two of the visionaries are beatified. If that's not approved what is?