Why VPN can’t replace Wi-Fi security

Every time the subject of wireless LAN security comes up, people ask me about VPN as a solution for securing Wi-Fi. (Wi-Fi is the common marketing name for 802.11 wireless LANs). I've always told people that VPN security shouldn't be a substitute for good Wi-Fi security, and I even posted a comprehensive guide to enterprise wireless LAN security, but a loyal group of VPN-only supporters has always argued for a VPN-only alternative. I'm going to explain VPN and Wi-Fi security as best I can and why there is a right time and right place for each architecture.