Bash isn't putting anything in /dev. It checks to see if those files exist (I've never seen them actually exist though), and if they aren't there, it just parses the string and creates a network connection as though they did exist.

Bash is not even pretending such special files exist: /dev/tcp/somewhere is only an elegant syntactic shortcut for requesting a telnet-like network connected pipe in a context in which a filename is required. For the child process, it's just a file descriptor.

I don't think it's elegant at all. Magically treating special strings in this manner seems like a violation of "everything is a file".