Quick! Emergency! Help! Americans want to steal our time! ;-)
I guess the real issue here is that for a long time accurate time keeping has been something most important to astronomers and navigators, for whom time synced to the Earth's rotation is important.
The US proposal is presumably to do with some other notions of time they want to measure, which don't need this. For example, I wonder about internet or Unix time. Does it add the leap second when necessary?