When you are looking at "used" memory, you are almost certainly seeing the total physical RAM used my the kernel and processes plus the amount being used a file caches and buffers. The system will deliberately use up a large percentage/most of your "free" memory to cache files off disk, etc - this then dramatically improves performance when accessing those files. Windows does exactly the same thing.
So your actual memory use will be significantly lower than that figure, meaning there is no call for swap space yet. Of course there isn't much point caching files in swap thus you get the situation you are seeing.