Virtually the entire thing.
The iPad Air introduces a 64-bit processor, 29% lighter, 20% thinner... and THOSE are the things, according to the author is what put the iPad over the top to now be a viable replacement for a laptop. That is simply not true. He also makes mention of iWorks being free. iOS iWorks is so simplistic that it is virtually unusable for anything other than the most basic tasks. So much so, that Apple released an update to OSX iWorks that is greatly reduced in functionality so as to make interoperation viable.
There has been no improvements in the iPad line that has drawn it closer to being a laptop replacement. From a hardware perspective, still very limited connection choices. From an OS perspective with everything being sandboxed, prevents it from being a viable laptop replacement. Limited printing still is something that iOS fans overlook.