This is deliberate- basically we originally had a single URL which wasn't very fault tolerant and had some other scalability concerns for us. So, while we couldn't move existing users of old WSDLs (and the API), we want everyone to use something unique as the endpoint moving forward.
The
content of the WSDLs are the same for every customer right now, and it's probably fine to assume they will be for quite some time, should you want to locally cache and reuse across instances.