I can tell you first hand experience of that. The foundation knowledge in CCNA is just average stuff which IMO anyone working in the technical aspect of ICT should know about already, but then the cert. gets specific with Cisco gear and IOS when it comes to the problem solving aspect. If you're going to get CCNA then it's only useful if you work in environment with at least one or two Cisco gear. Also you have to remember the cert expires every 3yrs if you don't renew. Not very useful for sys admins and engineers that only deals with basic level of networking in LAN environment or for network engineers that don't deal with any Cisco gears at all (but they all do, lol).
For a level1 helpdesk position you're required to follow the script and usually not allowed to engage your knowledge at all.
A better way to judge if they're morons or not during hiring is to give them practical tests. Starting with basic how-tos and working the way up to complex problem solving (depends on the position). Weeds out the incompetents in no time I find.
Then there's the communications test which are best left to the HR people.