It's true that the severely obese people can get away with losing more without losing organs/muscles, but loose skin is still going to be an issue.
Are you sure on this? My brother was losing faster than that and he didn't have any loose skin issues. My dad managed to lose 30 lbs in a single month and also didn't have loose/hanging skin. He started at around 300lbs I believe. I'm sure a good chunk of it was water weight, but still.
Also, unless the poster you responded to is very severely obese in the range of 400lbs, it's just going to be very difficult to lose weight without nutritional deficiences.
Again, my brother was doing this (He started 350) and didn't have nutritional deficiencies. But he's also a guy - which I expand upon more below

Realistically, people eating too much can still have nutritional deficiencies, but below 1200 calories is where this really starts to rear it's ugly head.
For example, if I, a 5'5" female weighed 300 lbs I would need 2500 calories a day to maintain my weight. This is not that much. I could at most cut my calories to 1200 beyond which I would be risking screwing up my metabolism, that would give me a 2.5 per week loss.
I wanted to comment on this because it's a common myth that you can 'screw up your metabolism' by dropping below 1200 calories. That's not really true, your metabolism pops up again when you eat more, there's not really a 'starvation mode' to speak of. ( ) The real risk of the sub 1200 calories is not enough nutrients and not enough protein (i.e. the organ and muscle loss you spoke of).
Also, you're using what's basically the lowest end of the BMR scale (female & sedentary) for your example. A sedentary guy at 5'10" and 300 lbs will burn 3000 calories a day just sitting on his butt. For him, losing 3-4 lbs a week is still quite possible while staying above 1200 calories. If he does moderate exercise, he maintains at 4000 calories a day (yes - I am very jealous).
It might not be practical at all for you to lose 4 lbs a week (and I never managed more than 3lbs, and I imagine some of that was water weight) but it doesn't mean it's not reasonable for others - especially larger males.
Also if I were 300 lbs, I probably would be unable to do any significant exercise without risking serious injury. So I couldn't go ahead and burn 1000 calories a day by say running for 1.5 hours. I could walk or swim for a half hour, maybe burn another 250 calories raising the loss to 3 lbs per week.
Someone who can work out a lot wouldn't be limited this way obviously, and running for 2 hours a day as well as eating 500 calories less than maintenance would probably easily give someone a 4lb /week loss.
I think also it's easy to underestimate the amount of calories that can be burned without risking injury. I can burn an extra 200 to 300 calories in a day simply by making it a point not to sit down when I get home. Supposedly the difference between the number of calories you burn while sitting down compared to standing up for an hour is the equivalent you'd burn by walking a mile. And just about anyone can walk. Now, I'm not saying someone who's 300 lbs and out of shape is going to be burning an extra 1000 calories a day. But an extra 500 is not really all that unreasonable - which works out to an extra lb a week.
I'm not advocating huge deficits, however I know that when you're starting at the beginning of the weight loss journey, seeing substantial progress can have a
huge impact on your motivation. That's why even the Mayo Clinic's new diet book includes a 2 week 'rapid weight loss' section at the vary beginning - to demonstrate that you are capable of losing the weight, and not just at a snail's pace, Apparently their trials revealed that the confidence gained was an important factor in whether people were able to stick with the program.