The DMV I got my license from had an employee at the entrance to sort you into the proper category and check to make sure you have the proper documents. Not that this was 100% effective. Not all the tellers would agree though and would require extra documents you didn't have.

One teller required my social security card even though I had a current US passport with me.

Isn't that against federal law (to require a SSN for anything)? Even the IRS is willing to give you a different taxpayer ID number, if I recall right.

I don't know what state that was but when I lived in Virginia, "but 911" trumped nearly everything when it came to getting a drivers license.

What would be the point of the SSN if it were illegal for anything to require it?

Anything besides Social Security itself, that is.

It's a stupid system. Technically only the social security administration itself is allowed to require an SSN. But most banks, companies, etc. do require an SSN from you, or else they put you through a ton of hassle. In practice almost everyone just gives his SSN, and the few who don't can be subjected to more scrutiny. SSNs are also reused after you die. After all, we don't want to run out of numbers, our nation's greatest resource.