> Isn't it useful to avoid accidental change while open files with editor for just reading?

Why would that argument apply to a binary file (and only to binary files)?

> Is there any real world problem about read-only library?

It makes it slightly harder to remove a Python installation. Depending on the OS, you'll get a failure or require some additional confirmation.

Furthermore, it's very non-standard. Even if that's not a problem by itself, Python should just install things in the standard way.