Grandstanding and fear mongering
The FCC's authority over WiFi comes from the airwaves, which are a public resource/commons. They have no authority over private agreements.
The *ONLY* reason Marriott was made to pay a fine was that its particular method of stopping people from using hotspots was to spam spoofed deauth packets over the wireless. It is illegal to operate a device that interferes with other users in the 2.4/5GHz unlicensed spectrum in the United States, and the FCC is the public agency tasked with ensuring that devices and their operators comply with these rules, which are basically grounded in a combination of ancient public policy theory (unlicensed spectrum is a commons) and technical operational theory (no device should interfere with any other device's use of the spectrum, as far as that is technically possible).
Going around, passively sniffing the wireless, and asking users to leave? Not the purview of the FCC. Also note that this is a hell of a lot more work, requires training, doesn't fix poorly planned WiFi deployments, and is expensive.
Perhaps we will see venues start to adopt this. My guess is that we won't. Sending out deauth packets is a feature often included for free as a setting in a WLC. Procuring specialty equipment, training security or other enforcement personnel how to use it, staffing events to enforce the ban, and hiring lawyers to write it into the contract to cover asses appropriately are all vastly more expensive than a free feature in a WLC.
So Kieren, I hope you choke a little on your mild outrage soup. You might see this occasionally at high profile events with extremely pricey WiFi, but otherwise, the juice just isn't worth the squeeze.