Cyclocross bikes traditionally have used bar-end shifters. When riding across dirt/grass, you had to keep your hands on the bar because taking your hands off to shift (on down-tube shifters) was a sketchy proposition with all the crud that catch your front wheel and take you down. Since these were primarily racing machines, the hands were kept in the drops. So, bar-end shifters were the solution. Even still today, they have a following.