It simply depends on the art style they want. Of course vector is easier to draw and and scale up but it also greatly reduces the complexity of the artwork and the ability to do high quality textures & shading. If you are making raster artwork you want to make it huge to begin with. It can be extremely difficulty to duplicate artwork on a large scale in high resolution. I do a ton of vector work as well but from what I have seen on here people generally enjoy the skeumorphic coin/bar look so that is why I went that route.

I am curous to hear what OP has in mind.