I just got my Move stuff and Sports Champions, so I'm not sure, but having played a little of it before at a friends, I'm guessing maybe there's higher wind and things of that sort. That's just a total guess though.
To the mattresses. PSN: Justice_98405, Xbox Live: Justice98405
I think there are some differences like more wind in the higher levels, but the biggest difference is the starting locations.
The starting locations are further back with each inreasing difficulty level, so that the courses are a lot longer. At gold level, there are only a few courses you can make it to the goal on your first throw.