Arch Linux

I don't know how did you get this, because it works for me. Maybe you created a symlink from /usr/bin to /usr/sbin on your system?

$ ls -ld /usr/bin /usr/sbin
drwxr-xr-x 6 root root 180224 29 jun 18:00 /usr/bin
lrwxrwxrwx 1 root root 3 30 sep 2015 /usr/sbin -> bin

I think I found it.

$ sed -ne '56,70p' /usr/bin/urlwatch
# Check if we are installed in the system already
(prefix, bindir) = os.path.split(os.path.dirname(os.path.abspath(sys.argv[0])))

if bindir == 'bin':
# Installed system-wide
examples_dir = os.path.join(prefix, 'share', pkgname, 'examples')
else:
# Assume we are not yet installed
sys.path.insert(0, os.path.join(prefix, bindir, 'lib'))
examples_dir = os.path.join(prefix, bindir, 'share', pkgname, 'examples')

urls_yaml_example = os.path.join(examples_dir, 'urls.yaml.example')
hooks_py_example = os.path.join(examples_dir, 'hooks.py.example')

$ echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin
$ ls -ld /usr/bin /usr/sbin
drwxr-xr-x 6 root root 180224 29 jun 18:00 /usr/bin
lrwxrwxrwx 1 root root 3 30 sep 2015 /usr/sbin -> bin
$

And so urlwatch discovers itself at /usr/sbin/urlwatch, which it fails to detect as a system directory.

The solution is to hardcode assuming system-wide installation, since my PATH is my own business.

It's your own business, but if it's nonsense and that's what's causing the issue, that's your business as well.

It's a perfectly sensible setting. What is nonsense is a package checking at runtime whether is installed system-wide, when it always is.

No, having /usr/sbin in path is certainly not sensible and is non-standard.

You can ask upstream developers to accept /usr/sbin as well when it checks if it's installed in the system:
https://github.com/thp/urlwatch/issues