Do Not Call list?

A couple years ago, I put our phone number on the national Do Not Call list in the hopes of keeping telemarketers at bay. Despite that, every night almost without fail, we get one, two, or last night three calls who come up on the caller ID as 'restricted' or 800, 888, 877, or 866 numbers. We usually let this go unanswered and the caller seldom leaves a message. But last night, already agitated by events unrelated to the poor sap on the other end of the phone, I decided to answer one of the calls.

Me: Hello
Hapless Telemarketer: (long pause while their system figures out they've got a live one) Hello, can I speak with Jeanne Moran?
Me: Who's calling?
HT: This is so-and-so from blah-bedie-blah energy. I'd like to speak with Jeanne about our company's...
Me: Do you know we're on the national Do Not Call list?
HT: ~silence~
Me: Do you know that means you're in violation of the national list's rules?
HT: ~silence~
Me: -> hang-up ->mumble to self -> resume dinner prep

The point is - what's the point? Why does the list exist if companies ignore it? Maybe there's fine print about who can and cannot call despite the list. Maybe there are exceptions.
Or maybe I'm getting a taste of my own medicine. Maybe companies look at that list as guidelines, the way I look at the speed limit 65 sign and set my cruise to 71.