This will probably not work, if a non-wordpress webdir contains a directory named ‘wp-includes’.
Those webdevelopers were probably smoking pot anyway 🙂
web01:~# find /var/www/virtual -type d -name wp-includes | xargs -n1 -I{} -i bash -c ‘echo {} | cut -d/ -f5- && grep \$wp_version {}/version.php && echo’ | less