I thought they stopped requiring that years ago. I must have just had that in my history and didn't look closely.
If I remember correctly, some DNS systems will automatically add the www if the system can't find the site without the www. So if you type in acme.com, the DNS system will try to find acme.com, and if it can't find acme.com it will add the www and try again to see if it can find
www.acme.com. Or some systems will just redirect acme.com to
www.acme.com.
