I believe there is no difference between vCenter licenses across windows & appliance.
You will get vCenter license (as whole) and now its your choice to deploy vCenter either on windows or deploy the same as appliance. Once deployed you need to apply the license.
If you go for vCenter foundation, you will get same set of features either you deploy the VC on windows or as appliance. Same applies to vCenter standard license. If you deploy on windows, you need windows license as well.
Refer: Buy VMware vCenter Server: Management for Virtualization Systems | United States
Let me know if you need clarification