At the moment no, items cannot be deleted or hidden from the purchased list (and that applies to other types of content as well e.g. apps). You can try leaving feedback for Apple : http://www.apple.com/feedback
You can now HIDE (not completely delete) a previously purchased item from the iTunes in the Cloud list. In iTunes on your computer, go to your previously purchased list in the iTunes store, hover over an item and you will see an "x" in the top left corner of the item to HIDE it. This can also be done on an iOS device by going in to iBookstore (this also applies to iTunes or the App Store), going to your purchased list, and swiping across an item. This will bring up an option to HIDE the item as well.
*Note that both of these methods DO NOT completely delete the item from your previously purchased list, but it will hide it from view. To unhide it, you can go to your account information page in iTunes. There is a section for iTunes in the Cloud, and "view hidden purchases."
I noticed this after I upgraded to iTunes 10.5 and iOS 5.0, so I don't knnow if this feature is only available for the newest versions or if it can be done from older versions now as well. Someone that hasn't upgraded yet might be able to tell us.
I hope this helps.