The Flash 9.0.0 plugin or higher is required to view content on this page, but was not detected on your browser.
As far as I know, there is no reason why street curbs are as hard as concrete. In former days, people probably didn't have different materials, but today?
Hard curbs only ruin your car tires, and if there's a street festival and you end up sitting on the curb for a while, your behind will start aching in no time at all. So why not make street curbs from a material that's softer, yet durable and easy to clean?