Well, from a quick scan of fare availability on the Rex website they haven't exactly shot the lights out on day one of their sale. Plenty of $79 fares (actually $85 if you want to be able to pick your seat) still available on a variety of flights on 1 March and onwards. Bearing in mind that Jetstar sold something like 70,000-80,000 fares in six hours when they launched their big sale back in June Rex's 100,000 discount fares 'launch' appears to be somewhat ambling in comparison.
To whoever was wondering why Qantas and Virgin weren't reacting, this is why.