Exactly how credible is an article like this? Outside a few key people at Amazon no-one knows how many Kindles have been sold, how many have been produced, nor anticipated sales in the coming months. As far as we all know Amazon could have sold just 1,000 Kindles and paid a bunch of uni students to post on random forums about how much they love their Kindles (ok very extreme).
I agree, sales may slump with the Kindle, anyone who has one is less likely to upgrade, especially those who have a K3 as the new offerings whilst tempting aren't as big a jump from the K2. The release of the Kindle Fire may have had an impact, but financially less people have spare cash. By what negative impact this has, I do not know, but un-released figures being made up by people in an online article IMHO are meaningless.