I admit that was pretty much an over-generalization - it's what I get for trying to respond quickly... what I should have said was that the higher your BF% the more of your weight loss tends to be from fat and not muscle. I.e. someone who's morbidly obese will tend to lose more fat than muscle even if they're not exercising.
If you don't have a lot of muscle for your height/frame it's also a lot easier to gain it than it is for someone who's well trained/has already deliberately built muscle.
So while it's not impossible for someone who's 300 lbs to diet down to 200, lose lots of muscle, and then eat their way back up and not gain any muscle back... that kind of implies that they did something different the first time they gained their way up to 300 lbs. Otherwise... why would you expect that they'd have gotten muscle while gaining weight to begin with?
In any event, while it could all come back as fat, and certainly there are good reasons to work out, I don't think that the average guy on the street has to worry that if they eat at a deficit for a while they're going to 'ruin their metabolism' somehow. If they're not working out anyway, then just the normal cycles of surplus and deficit (since few people graze all day long and maintain a constant supply of calories) is as likely to have people replace fat and lose muscle as deliberately dieting is.
Soooo, much longer response to say that no, I still wouldn't think it's something that people should need to be aware of on a constant basis.
(The 6 to 10 calories and not 50-70 per pound of muscle is accurate though!)