Since the Kyuubi is the strongest of the nine Bijuu, an extreme amount of chakra is needed to hold down the beast's enourmous chakra, which is one of the traits of the Uzumaki. Also their long lives (pardon any unforseen mishaps like Kushina, who must have been in her 20s) allow them to have the beast reside in them for longer periods of time, and since their sealing techniques are seen as perhaps the best such techniques in the Naruto universe, the seals are strong and resliliant. It could also have something to do with the fact that the Uzumaki's are in a stronger releation to the Sage of 6 Paths then most others as well (they say it's in relation to the Senju, but since the senju are related to the younger son, who is the son of the Sage that automatically give the Uzumaki's relation to the Sage as well).