Contracts do not work that way.
Electronic media does not work that way.
Think it through.
I write a song, which will be sold exclusively through your online music retailer in mp3 form. I give you a copy of the mp3, and you allow people who pay you money to download that mp3. Then we split the money.
Lets say that our contract requires 30 days notice before cancellation.
How can I "pull the plug?" Lets say I order you to stop selling the mp3, and I don't give you 30 days notice. What do my words accomplish? You still have the mp3, and the right to sell it. What can I do? Its not like the data is piped from my master server to your customer. I can't turn it off like water from a faucet. I can't sue you either since you have a valid contract. My words are just talk.
One of the following scenarios happened.
1. WOTC didn't have a 30 day notice clause for terminating the license. They had a much shorter period, maybe even 24 hours, which they followed. I suspect this one as most likely.
2. WOTC did have a 30 day notice clause, and offered RPGNOW and the other retailers a new, more lucrative contract in the future if they agreed to cancel this contract now. RPGNOW decided that breaching their contracts with their customers was the better choice, terminated their current contract, and accepted the new one.
3. WOTC did have a 30 day notice clause, and gave notice 30 days ago. No one told the customers until today.
And I suppose, for the sake of argument, we can include:
4. No one at WOTC, Paizo, or RPGNOW has any clue what their licensing agreement says.