The biggest problem with the Russian's plan is that while the object's orbit is still in doubt, any action they take to change its orbit could end up making things worse and not better. The chance of that happening are very small, but they're still there. On the other hand, if it was going to hit us, the earlier we act, the better, so it's sort of a 'damned if you do and damned if you don't' situation. Russia has much more incentive to do something about it than we do as well, since the projected course across earth's orbit carries it over most of Russia. The US is not in it's path, so we have less reason to do anything about it.
If you build a man a fire, he'll be warm for a day.
If you set a man on fire, he'll be warm for the rest of his life.