All cars fly, and all buildings are miles above the ground, standing on stilts. The ground is rarely, if ever, actually shown. It's been theorized that maybe the world flooded, or went through some environmental disaster. (A Harvey Birdman episode joked that they lived so high up because the ice caps had melted and flooded the earth.)note Actually, in the original 1960's series, ground level was shown on a few occasions and it was perfectly fine, with trees and grassy hills. The whole idea of an uninhabitable Earth's surface in The Jetsons came in the 1980's revival, when the Green Aesop trope was popular, so the 1990 movie shows people all living above a thick layer of pollution.
It would appear that the only human ethnic group to survive into the future were Occidental. Worst case scenario: the result of racial cleansing via historic war or genetic modification. Only applies for the original TV show. Later additions would throw in a Token Minority, most likely because someone took note of this rather unsettling environment.
George is forty and Jane is thirty-three. Judy is sixteen. This means that George was twenty-four and Jane was seventeen when the latter became pregnant with her.
In the second season: the family is watching TV one night and learn that the priest who married George and Jane was actually a con-man, and that this one thing somehow meant they were never actually married. This not only means Judy and Elroy are bastard children, but that their government is a theocracy, likely Christianity or one of its derivations. Were other religions driven to extinction in this universe? And what about people who aren't religious?
Fridge Horror / Tear Jerker: In this universe, The Big Show was frozen for a century. When news of his disappearance came out, wouldn't WWE investigate? What about his Real Life family? Assuming they exist in the Jetsons universe, how would they have felt? Had Elroy's time travel equation not played a part in the plot, would it have turned into a Futurama-esque situation?