another thing you could mention is students, young people or just people perhaps living in temporary rented accomodations which don't have the physical space to have a desktop + desk + PC monitor around, or if they move a lot due to work or financial conditions it's a hassle to carry around. A bin bag of clothes and laptop bag is easier...
+1 even a busy house with kids running around, you may not have a permanent office for a desktop, or want cables running all over. A desktop replacement can be put away or quickly moved to a free room. The only real issue is the price for one that can game.