When flagging a question as off-topic: not about Ubuntu (through this path: should be closed ..., off-topic because ...), the following text is displayed as an option (emphasis added)
This is not about Ubuntu. Questions about other Linux distributions can be asked on Unix & Linux, those about Windows on Super User, those about Apple products on Ask Different and generic programming questions on Stack Overflow.
The Super User What topics can I ask about here? page lists the following to be on topic:
- computer hardware,
- computer software, or
- personal and home computer networking
That page doesn't state anything about Windows. Surely, there are a lot of Windows questions, but Windows is not main subject (as it is included in the three points above).
So my point is that the wording "Windows questions belong on Superuser" is too focussed on Windows. A better variant could be "Software questions not specific to Ubuntu belong on Superuser, including questions on Windows"
I struggled over this while reading this question about Thunderbird. The question is not specific to Ubuntu, but is a general software question. So it should belong on Super User. However, when I flagged the questions I was not sure if flagging "This is not about Ubuntu ..." was the right flag. The question is not Windows specific, so I searched for a better flag (which does not exist).
This led me to the conclusion, that the flag text should be reworded, for example:
This is not about Ubuntu. Questions about other Linux distributions can be asked on Unix & Linux, those about Apple products on Ask Different, those about Windows or general software questions on Super User and generic programming questions on Stack Overflow.