Seeing things from both sides, there's the obvious sheer number of aircraft which sets them in a different league to us, also don't forget ATC are talking to each other coordinating departure & arrivals. What we as pilots hear is only a fraction of what these guys & girls do. Yes, it would help if they slowed down, but with the volume of aircraft & comms with other atcs, slowing down is sometimes difficult to do(even on a sub concious level). Even SY controllers deliver they're instructions rather quick at times. Not defending the US ATC but all organizations, airlines & government sectors find it difficult to keep up with the times & growth throughout the world. Vigilance is the best defence.