The Wiki entry is correct - Majors are where you can get the most points in the world rankings.

Now, why the PGA Championship is a major is a mystery to me. IMO, it's nothing more than 'Club Champ' for the guys on the USPGA Tour.

Why not the Australian Open? Or the Canadian Open? The only reason it makes sense to have 3 of the 4 majors in the US is money.