Yep...moving every 2 years... I found sleepovers to be very regional. I had the most in south carolina and southern california. TONS. Often weekly. In SoCal we found that in our area school night sleepovers were commonplace as well. Coming home afterschool, doing HW, playing, taken to school the next morning. ((Never found that to be the norm anywhere else)). In OTHER states and places... maybe a sleepover bday party, but that was it. So once or twice a whole year.
Sometimes how many sleepovers was linked to how "popular" I was (which varied tremendously... I've been both queen bee and social outcast... still the same person, me, just different schools) and sometimes not. I had tons of sleepovers in soCal, and I wasn't a popular kid there... it was just the "norm". Instead of arranging playdates, parents arranged sleepovers.
For my own son... we've had loads of "piquito" sleepovers (aka until 10pm-midnight)). And parents come as well. Essentially a dinner party where the kids get in jammas and sleeping bags and watch movies and play while the parents hang out and then are carried home asleep. But we've yet to have a "real" sleepover. Although he and one of his besties are trying to get one going.
I don't know whether the lack of sleepovers here is a regional thing, or if parents have just gotten less relaxed, or if the preponderance of scheduling (from both activities AND from most families now being dual income AND for about half of the families out there being divorced) has just made it difficult (saturday games, parents working, having to pay for daycare even if it's missed, having limited family time, etc.).