What about using NFC smartphones instead?
The problem with using NFC smartphones instead of wristbands is that not everyone has one. This alienates ticket-holders and brings contactless participation down from an achievable 100 per cent if you issue every attendee with an RFID wristband.
Then there's the fact phones run on batteries, and unlike RFID wristbands, will run out at some point during a multi-day festival. And, with limited (sometimes non-existent) ways to re-charge your phone in a field, your e-wallet, e-ticket and the ability to brag to your friends on Facebook, will vanish.
To say there's no place for NFC at festivals is wrong though. The Samsung Galaxy S4 for example, has been used as an RFID reading device and it's a perfect hand-held scanner for smaller events.