I think the main reason to 'brush' the concrete is to make is less slippery (mostly when wet).
You could probably have a polished mirror finish if you wanted it, then you can ice skate all year around.
My guys did NOT charge any extra for the 'wet' release stamp. It is literally a big rubber stamp they beat into the concrete with a stick (with a big flat metal plate on the bottom).
http://youtu.be/8l_bOUvhqQU