These are the three things that WiFi still can't compete in against a wired network.
Even the most secure wireless is still much more susceptible to attack then a wired network. Even with the most modern access control and protection methods (which are neither cheap nor convenient) the sheer massive avenue of attack WiFi presents creates a problem for many large corporations. Ask JPMorgan Chase how much WiFi connectivity they have. Or pretty much any US Government building.
Even if you do as the article suggests and call in an expensive contractor to map out the best locations for access points, you have to find out if it's even feasible to run network and power to that location. Even with the best-possible placement you are going to have dead zones, and the size and location of dead zones will vary depending on the devices used. My Toshiba laptop got service in places a virtually identical Macbook did not- let alone the poor wireless reception most mobile phones and devices provide. So you have to deal with irate users, and try to find places to install additional access points to cover the dropped zones.
When I worked for a small non-profit K-12 school, during teacher inservice days I always had to install 2 additional access points in the gym so that the teachers could all connect on their laptops, as the single AP currently serving the gym was not sufficient. Even then, transferring any large file from the server or online either brought the network to a standstill or required tethering each machine to an ethernet cord to do the transfer. Most high-tech oriented conferences, the wireless is all but useless if it's available publicly, due to the hundreds of devices all connecting within a limited frequency space and bandwidth. There is just not enough bandwidth in a small space available to deal with more then a handful of data-rich connections. Spread across multiple spheres of AP reception the problem is reduced, but not eliminated! My bedroom is WiFi-connected only due to wiring constraints and connecting from my laptop to my server via VNC or to copy files is very... very... slow. And really, try having a LAN party over wireless- I can run hundreds or thousands of network cables through a small room and connect everything I need for nearly any project or task inexpensively, and know that the network will be robust. Working with WiFi in anything other then a solo arrangement is a lesson in frustration.
TL;DR - Until security protocol and access control methods are more robust and available; until tools to design, implement, and test wireless networks are more plentiful and robust; and until bandwidth availability is not on par with but exceeds that of standard CAT5- wireless is but an adjunct, a convenient add-on to the main structure of a wired network in a business. ... err, not that I'm impassioned about it, or anything.
