That's the same for every device, in release builds (such as your 18.06.5), yes. In the sense of list listen_http 0.0.0.0:80 and list listen_http [::]:80 --> listening on any IPv4 and any IPv6 address, requests from WAN are rejected by the firwall configuration.
On snapshot builds, no - indirectly, as no luci/ uhttpd are installed in the first place.
I just discovered that the problem with the LuCI's HTTP server not answering on the LAN interface after reboot and until uhttpd is restarted, only occurs when I try to connect to LuCI's httpd service from hosts outside of the LAN network 192.168.1.0 / 24. For example from: 192.168.0.4.
I have the LAN interface of the router configured as 192.168.1.1 / 16.
Note, that the 16-bit mask makes the host 192.168.0.4 reachable from the router ...and as a confirmation of this, I can connect via SSH from 192.168.0.4 to that router at 192.168.1.1, without any problems.
Why does the HTTP server have a problem replying to 192.168.0.4 but the SSH server does not ?
The problem disappears after I restart the uhttpd service with:
/etc/init.d/uhttpd restart
...Note, that before and after that restart, I can see the following process running with identical parameters, except for the process id.