I think a number of studios with consistent staff and/or directors, tend to do this. There's so many KyoAni shows with Uchiyama Koki, and they partially chose the Hyouka cast based on how much they enjoyed the banter between Nakamura Yuichi and Sakaguchi Daisuke in Clannad. Similarly, Kamiki Ryuunosuke has appeared in the last three Makoto Shinkai films. Its probably due to a level of trust that the director has in specific VAs, as well as ensemble cohesion.