As other people said, it does save the forum owners and admins various legal headaches by using such a system.
Normally the only people I see complaining about it are people like you - the unverified. You're in Toronto. You should be able to find a verifier at a game pretty dang easily.
Moreover, the people verifying aren't "kids" but usually respected members of the community. You're willing to go out and play a game but you aren't willing to see if a verifier will be there, or if one might be available to take a quick peek at your driver's license down at Tim's? Are you lazy?
Another point is that they do verify the age of the account holder in question, making private transactions easier.
Sure, I can verify someone's age myself in person. But I am in Ontario. What if I am selling a gun to someone in BC? Do I Skype them and ask them to hold their license or health card up to the web cam? Seems like a good way to get your identity stolen. Seriously.
This has to be a troll account.