If you do a little digging into the Amazon top-sellers, you see that the XBox One above PS4 is the "Day One Edition". That's the one that ships to you the day its released. They are still available for order. Sure you can consider that PS4 has bundles still up for pre-order, but xbox doesn't (from what I can tell on Amazon, as that is the only site you seem to trust) so, it's not really fair to consider anything other than the basic launch versions of each console.
PS4 launch edition is sold out, so how can they continue to be ordered to even keep its placed in best-seller?
Now we consider the standard edition of both consoles. The standard edition of the PS4 is in the top 10, where the standard edition XBox One doesn't even make it onto the top 100.
PS4 held the top spot until they sold out of launch versions. Of course the pre-orders would "sharply decline". There are no more to pre-order.
You are blindly posting articles to try and prove your point, when (considering this is the Internet) the information from those authors can easily be stretched, skewed, manipulated, what have you.
I did my own research, and from what I see, the number of pre-orders is simply an inventory issue. Then we looked at the standard edition to see that the PS4 is still in fact being ordered and is vastly ahead of the XBox one standard edition.
Finally, the PS4 launch edition has sold out whereas the XBox One launch edition has not. What does that say? Consider the article Punk posted from the same website as your article saying that there were more PS4 systems for order than XBox one.
A source:
http://www.amazon.com/best-sellers-...=ATVPDKIKX0DER&pf_rd_r=00ZR4RYVEA88P6Y0VCK5#1
It is updated hourly, so my information is accurate as of 6/29/2013 11:14 AM EST.