Wrong. It's about being able to do your job, and ideally do it well. Anything else is just Bullsh!t (of the brain-baffling variety).
I'd rather have an overweight lump with a brain and the sense to use it than a muscled moron in the back of my aircraft.
Obviously to make up for the lack brain you have.
If all you are after is 'just being able to do your job', poke off to SleazyJet.
Yet again, its not about being a bronzed, muscle bound adonis, its about setting a vaguely military like standard that the young chaps can look up to. Being a fat wheezy knacker with a sick note from matron doesn't exactly set you up to be classed as a cut above the rest, does it?
I'd rather have a capable bloke with a brain who wouldn't become a liability if I had to start doing a Billy Whizz away from the teletubbies somewhere sharp.
As has been said already, someone who doesnt have at least the basic personal discipline to stop being a fat bloke is probably lazy in the brain too.