ITV2 probably push on-demand more because that target market, 16-34 is more likely to be using it or know about it, plus I dare say its probably more of a reliable way to track exactly what's being watched and when its being watched as opposed to tracking viewers through the traditional BARB system. BBC iPlayer for example reported an episode of Peter Kay's Car Share racked up 2.4m viewers on the BBC iPlayer alone excluding Virgin/Sky requests. Add in requests from Sky and Virgin and whatever else, that's probably another quarter of a million catch-up views for that show.
Continuity/Media Planning strategy has changed to the point that, using a 'Next' on an ECP
during a show like Love Island is less effective, than pushing On demand services. As that demo will be watching ITV2 through live streaming.