Unbelievable.
Come on, I'm asking a question seriously, so please answer me seriously.
1st off...
http://bit.ly/1av4x4KThere are many reasons why someone would want to own a pet.
Anything from having company, having an exercise buddy (as CV mentioned), having something that will always be excited to see you when you get home, they will never hold a grudge against you, you could talk to them all day and they will never repeat anything you ever say! They also will protect you in any way they could, weather waking you up because of a fire or scaring away a burglar.
There are many more reasons but those are the few that popped into my head.