The Rabbis teach that the soul is judged anew each year on the Yahrzeit. That is one of the reasons why the family recites Kaddish and learns Torah on the Yahrzeit, to try and elevate the soul of the deceased. By involving themselves in spiritual pursuits the family is helping to alleviate any negative judgments that might have been passed on the soul.
There is no obligation to travel a distance to be at the grave for the Yahrzeit. In fact, there are some who are of the opinion that the money that would have been spent on such a trip would be better used for Tzedakah (giving charity) to help elevate the soul of the deceased.
