The cabin crew aren't made of sugar - they are perfectly capable of retrieving lost devices. If it were me, I'd be first on the floor to find my own fallen item, but if an FA lent a hand, I wouldn't refuse nor think it's beneath his/her job duties. An FA is on board primarily for the safety of the passenger complement, and as we have an identified safety (fire) hazard with electronic devices in crevices, it's one of those 'part of the job' things we all do during the course of our day. They wouldn't offer if it were unsafe, inconvenient or merely gross to do so.
Also, a moment of inattention, carelessness or being unaware of the possibility of losing a device does not make a passenger stupid. There likely isn't a mobile phone user on the planet who hasn't inadvertently dropped it at some point.