I sometimes think the whole "make me an omelette" or "roast me a chicken" test to be a little outdated. There is a wide culinary world out there are not everyone is good at everything. I kind of look at it as a decent litmus test, I suppose, but I'd be more interested in (like I said earlier upthread) if they can cook a steak to medium rare and give me a nicely cooked piece of salmon or bass.
Not everyone went to culinary school, trained through a formal brigade (especially nowadays) or is keen enough at home to learn how to make a perfect french omelettes. Maybe they never worked brunch so they don't know how to do a hollandaise.
Cooking encompasses a lot of techniques, disciplines and styles. It is perfectly reasonable to think that not everyone who is a good line cook can make an omelette, or roast a chicken, or make a hard boiled egg.
I know a guy who is probably the best grill cook I have ever seen. Beyond being a hard worker, fast, etc and all that, he cooks just about damn near everything correctly (when he does have a steak or chop come back, it is usually because the guest wants it different than how they ordered it). But I'm pretty sure he couldn't make a french omelette. If course, my point if moot if the job he is applying for requires him to make omelettes, but assuming that is not true than it might be easy to overlook someone like that if they fail the test.
I think a lot of places ask for a trail, too. I've never got hired as a line cook without doing a trail, but I only had to cook for my job (meaning make the chef a dish to eat) once I think.