DMZ can probably tell you more about her dogs. But in my experience, if the dog's hair has any curl to it and it is cut really short it might have a fluffy, sort of curly look to it. Catcher has a ton of hair and if it were not tied up it would stand out straight all over his head sort of like a fluffy chow. Dogs with very fine silky hair probably don't have a "fluffy head". Kallie's hair is more on the silky side, especially her head and ears, so it is not at all fluffy.
Peanut has the biggest cotton ball head after blow drying. I always assumed it was his type of hair, more cottony than silky, and the length. It may not be long enough to 'weigh' it down more. I'm growing Peanut's hair a little longer now (mostly because I'm too lazy for a heavy duty groom session) but lots of people make fun saying that his fluffy head looks too big for his little body. It does seem to settle down after a few days, but he'll never look like JMM's Mikey.