To me, upstairs is the main level.
The main level of the house looks like some old guy lives there, maybe watches TV and/or reads a lot. My library is in one bedroom, the TV mounted on the wall with a DVD and old stereo in the living room, a tiny TV with a DVD and VCR in the keeping room, a dining room table with 4 chairs, and a very clean kitchen.
Downstairs, in the basement are the guitars, basses, amps, piano, PA system, pool table, computers, monitors, and a shitload of games.
So I generally spend most of my time downstairs on the computer or playing guitar/bass or playing pool or just kicking back. I will spend time upstairs reading or watching a DVD. I'm a hipster so "I don't watch TV"
Carl