If a household has only one computer with 4 active members, they will all be counted as one unique visitor. So, I believe this should balance out.
I'm not so sure it balances out. We are not in the 80's where technology is a rare luxury any more. Nowadays practically every single mobile phone has an internet connection and almost everyone has a phone. Even homeless people have mobile phones.
I myself have about 6 devices that can connect to the net. If I used each one 3 times in one day to access the site I'd be counted 18 times. That's 540 times a month! Now we can see how their figures can be manipulated to kingdom come.