Here is the text of an email that went out today from Paizo:
Wizards of the Coast has notified us that we may no longer sell or distribute their PDF products. Accordingly, after April 6 at 11:59 PM Pacific time, Wizards of the Coast PDFs will no longer be available for purchase on paizo.com; after noon on April 7, you will no longer be able to download Wizards of the Coast PDFs that you have already purchased, so please make sure you have downloaded all purchased PDFs by that time.
We thank you for your patronage of paizo.com. Please check out our other downloads at paizo.com/store/downloads.
The Paizo Customer Service Team
I have not heard why they pulled the PDF sales.
RPGNow.com has posted they are no longer allowed to sell WOTC PDFs either.
RPGNow Annoucement Regarding WOTC PDF Sales
I hope this is just temporary and that Wizards will move to some other method of digital book distribution. If they do not and only offer DDI subscriptions or dead-tree books for their content, then Wizards just made a serious mistake. Digital books and downloads are the future of gaming and they had better keep up or they will go the way of TSR. The other item on both sites was that you could no longer download previous purchases after a specific date. Not only have you stepped backword with your business model, you managed to anger your best customers. The blowback from the gaming community on this decision is going to be nuclear.
I truly hope this is not some feeble attempt to stop piracy that coincides with the lawsuits filed by WOTC against alleged pirates of their books. Even the RIAA is beginning to see the futility of lawsuits and whether or not you sell a PDF file, pirates own scanners.
Trask, The Last Tyromancer