As far as I know, you buy cable commercials through the cable company

not the shows. And they sell regional spots. So this national thing is making no sense to me.

Wrong...In fact Kieth Olbermann recently made fun of Fox News for running a commercial for a Mark Cuban film during an O'Reily show where O'Reily was slamming the film.

Total up the cost between one nationwide campaign, paying a single network, verses paying 3,000 local markets individually.

Which makes the most sense?

Believe me, for a big ad buy, they'll kiss your ass, too. They'll charge you full price, and then slide the time that was excluded over for resale by local outlets.

You can buy through networks as well. Example--The Superbowl. You buy those ads from the NETWORK. They're aired nationally.

It's "what's left" that goes to cables and local affiliates. FWIW.

Networks CAN "cut out" regions (for example, if an offer isn't legal in one state, but is in another) easily--they just dump that ad time to the local affiliate for resale.

You know how every so often you see a piece of a halfassed ad at the end of another? That's because the affiliate isn't synched with the "mother station."

but you DON'T want that ad to air in FL. They say fine, you demand a little discount, you haggle, they give it to you. They know they'll get plenty of money because the local affiliates (satellite or cable) will resell those blank spaces. If no one sells them, Florida viewers get James Earl Jones giving a "THIS.....is CNN" ad, or an ad for an upcoming show, or maybe even a PSA (public service announcement).

They type up the contract, which says when and how often the ad will air, and says that it won't air in FL.

Then, the ad salesman and the campaign media manager, or whomever, SIGN the thing.

That contract will tell you if it's a "mistake" by the network, or if the campaign rep didn't include that caveat, for whatever reason. It would also give us the name of the person who made the ad buy--and we could then ASK them if it was a mistake or deliberate, and if they were asleep when the DNC directives came down the pike...!

. . .the only reason you would by through the companies if you wanted to target a specific market. When you are going national you buy directly from the network.

That's why I was able to see Bush and Kerry ads in NY, even though NY was never competitive.

national is cheaper per thousand, but usually results in waste coverage

Network feeds have national ads, but there are also blocks built in for the local affiliate or cable provider to put in their own.