Υeah, those PC's in those images had to be like 10 years old never opened. The spiders were the scary part.
unfortunately for us pc service people, this is so wrong haha.
I have cleaned 3 times the last 2 years a laptop that managed to gather cat hair and pubic hair on all 3 times. The cpu fan stopped rotating due to the carpet of hair! so the customer (female) brought it for cleaning.
I have cleaned 2 times a Tower PC with 2 120mm fans with the typical filters on the fans, the dust inside was something else, in 8 months.
I have cleaned a laptop 2 times between 2 summers becaue the guy was taking it at the beach and was smoking weed also!
Burnt small lizard on a motherboard, i have seen it. PC Working after getting doused with coffee. It had no milk or sugar. Other laptop PCs that got coffee with milk and sugar OR WORSE coca cola! died after few weeks lol
Worse thing i heard. "I have my laptop on my bed, on the blanket, why does it turn off?" Guess why.. half the blanket's fabrics were inside the fan..
And many others!
A. The place you have the pc plays important role.
1) How close it is to the floor. The closer the worse
2) If its in a bedroom (more clothes, more fabric in the air, pc will need cleaning faster
B. Your activities on the PC area.
1) If you smoke
2) if you scratch you hair! well if you have pets, dogs cats..
C. How often you clean the area. Doesnt matter how dirty is your room but how often you clean it. PCs are like magnet to all the dust, considering they get galons of air through them with their fans.
D How hot is your environment. Hotter areas (like south Mediteranean, California or whatever) create more dust in the air and more pollen thus PC need cleaning more often.
PS On a sidenote, PCs that had no extra fans apart the cpu/gpu/psu and one 80mm fan in the back didn't get loads of dust in few years even. Makes you wonder, if you dont game, if fans are really needed apart the minimum ones.
Fanless systems would most certainly not get even the 10% of the dust that normal pc would get.