(Donning sysadmin hat...)

Regardless of whether that's true or not, it doesn't matter. If you set up your HTTP::Daemon on port 1433, it may not be vulnerable to the MS SQL Server worm that keeps banging on my door, but it'll be more of a drain on the server's resources for the HTTP::Daemon to wake up, determine that the incoming request is gibberish, and reject it than it would for the kernel to just ignore it because there isn't anything listening. Not to mention that simply having the port open might be enough to draw additional attention from people interested in whatever normally runs there. (Same argument applies to any other port, of course, I just picked 1433 because that's where most probes have been directed lately.)