From RPGNOW’s website:
Wizards of the Coast has instructed us to suspend all sales and downloads of Wizards of the Coast titles. Unfortunately, this includes offering download access to previously purchased Wizards of the Coast titles. We are in discussions with Wizards about their decision to change their approach to digital sales of their titles and will post more information as we have it. If you would like to let Wizards know your opinion on offering D&D titles for download, we suggest the D&D Message Boards found here.
It seems piracy has become an issue, as stated by WOTC_Trevor on the ENWorld boards:
Unfortunately, the truth is that due to recent findings of illegal copying and online distribution (piracy) of our products, Wizards of the Coast has decided to cease the sales of online PDFs. We are exploring other options for digitial distribution of our content and as soon as we have any more information I’ll get it to you.
Let’s see where this leads, although I’d be majorly pissed if I paid for a book that I couldn’t download now… This may be counter-productive folks, let cool heads prevail here…