Why the cost of different VM type is the same?

As you may notice from https://github.com/WorkflowSim/WorkflowSim-1.0/blob/master/examples/org/workflowsim/examples/WorkflowSimBasicExample1.java That the cost model of CloudSim is per Datacenter so it does not change base on the VM type. It is different to the popular Amazon EC2 model. However, you may always change the model based on your need and write your codes.