Great example! I read reddit via a browser written in C++ on a Windows machine (written in C++) or on an operating system compiled by a compiler written in C++.

Great example! I read reddit via a browser written in C++ on a Windows machine (written in C++) or on an operating system compiled by a compiler written in C++... or even an app written in Java. Software engineering still uses languages/tools from the first few years that it existed, so it's unlikely that anyone means "completely replace every single LoC inexistence" when they say "replace".