The mechanism you are describing about fat cells refilling vs making new cells, does not make sense. They have done studies, and the number of fat cells remain constant during adulthood, unless you undergo liposuction or other procedures. I think what you are describing is a set point weight, where your body tries (via hormones I think) to maintain its preferred weight. So its more a metabolism effect rather than physical space issue about storing fat.
Since you hold a strong opinion on the quality, can you give an example of an animated icon pack which keeps to good design standards?