When you are in larger sizes, it takes longer to lose a size. It took me forever to go from an 18/20 to a 16. In the last 50 pounds, I have been dropping sizes like crazy. So if those people were just 50 pounds overweight to start with and went from a 16 to a 6 or whatever, that would do it. Although that's really only 5 sizes, they would probably call it 10 and include juniors odd sizes to make it seem more.
I feel like size 14 is the magical- catch all size for me. I was 210, in a 14, now im 185, still in a 14, and I have a feeling I will be in a 14 until I get out of the 170's.
I have gone from a size 26 to 20. I wish I were in smaller sizes, but it still feels good to be dropping sizes, even if it's slowly. Posters have told me that I'm getting to the point where they started dropping sizes more quickly, so that's keeping me optimistic.
14s were like that for me too, but then I had an "aha!!!" moment when I realized that the reason I was 14s when I was in the 190s and 180s is because I really should have been wearing 16s in the 190s... I just couldn't bear to buy pants in bigger sizes than 14s.... so I wore them, even if they were tight on me.
When I started losing weight, they actually started to fit right, so I kept wearing them until it was clear I was a size 12.
Also, the rule of thumb is 10 lb per inch. But then the difference between sizes is one inch apart in regular clothes but TWO inches apart in plus clothes.
So to change from one plus size down to the next plus size is more like 20 lbs lost. (Still 10 lb per inch, it's just that there's 2 inches difference between a size 22 pant and a size 24 pant)
Don't stress over it. Just do what you are doing. If some stranger grabs you to look at your pant size, you have bigger problems (assault!) than pant sizes!
For me it takes an infinite amount of time to loose a dress size. Basically my chest just doesn't shrink ever!
My pants size went down as I lost weight (maybe every 20lbs?) but dress and me, well, that's another story. I tend to avoid them because it's really hard for me to find one that fits well.
Dress Size
Basically my chest just doesn't shrink ever! 
