Some of the characters with good incomes have great apartments (Gretchen, Wade, Robert, Sheila's second apartment). Daniel doesn't think his apartment is that great except for its garden space; Blaine admits he could be living in a much better place; and Blythe lives in a dump. The Jane Street town house came into the friends' lives via a couple of inheritances. Maybe because our characters are generally happy where they are, it's perceived that they are in great apartments. (Don't make us play the "It's fiction!" card.)