Virgin Blue, Jetstar, Ryanair and others all use the same outsourced reservation system, the front end web interface for booking is part of this system.
The hardware, software, data center are all fully provided and managed by application service provider. So the carriers listed above have little IT involvement in the running of the system apart from maybe making the web page look pretty. Although in the case of
VB, I believe they manage various components of the system in house, including the web interface, but it's all the same software.