No one should ever rely on the network layer for security, because networks are by nature insecure. Run traceroute sometime if you're curious to see how many nodes are located between your computer and your bank/stock broker/webmail. Every one of those nodes can see every one of your packets. The only solution is to use application layer encryption, and once you've done that, it doesn't matter who is spying on your traffic.
You'll notice that this study was done by "AirTight Networks, a wireless security company." In other words, they are fear-mongering in order to try to sell more of their products. No matter how secure you make your wireless network, it still won't stop anyone even 1 hop away from seeing all of your traffic. As security professionals, the researchers from AirTight Networks know this, which makes their study all the more stupid and despicable.