There are plenty of people I know who would fall for this, because they simply don't know. They were issued a laptop for work and were told it was secured through a VPN, but don't understand how networks or routing actually works. They think they're secure only because an expert told them that VPNs are secure.
Of course, you expect the tech folks at the RSA conference would know how it all works, but a significant fraction of the attendees are not tech employees. There are no doubt many finance people; executives with expense accounts and instructions to "come back with a security contract"; salespeople; politicians; and the press in attendance.
I just hope the guys with the rogue access points are no worse than gray hats who are posting them on a Wall of Sheep somewhere at the conference, and not actually hacking the attendees.