As with all services provided on Virgin's platform, its up to the broadcaster to decide what programming is available, & how it is accessed. Apart from the BBC iPlayer, which the BBC have provided a TiVO app to access their own internet playout facilities, all the other terrestrial broadcasters are just depending on the programmes being uploaded to Virgin's own Headend server network.
Considering the problems there have been with the iPlayer app since the start, its perhaps not surprising other broadcasters are reluctant to go down the BBC's route.
Cable customer since 1993. Services: FH TV, Sky Sports & Movies (2xV+), Talk Unlim Telco, VIVID 100, Virgin PAYG Mobile