As I understand it, the "Seven Kingdoms" refer to the kingdoms before Aegon's Conquest. Aren't there more kingdoms around the time that the first book is set? (For example, the Iron Islands and Riverlands are now two kingdoms, right?)
So why does everyone refer to there being seven?
For example, Robert says to Ned:
"In the South, the way they talk about my Seven Kingdoms, a man forgets that your part is as big as the other six combined."
If there ARE still Seven Kingdoms, and I'm wrong, which are the contemporary Seven Kingdoms, and which are the Houses that rule them?