I'd agree that PR is probably a factor in the University's creation of this department, but I've met a number of people who work there and they are honestly genuinely passionate about generating awareness and action - both amongst the student body and staff at Macquarie.
Promoting sustainability to students may not make a massive impact in the short-term - but students are the future employees, managers and families that need to be behind this issue. I agree 100% with promoting student awareness, since in the long-run as a collective they are the ones most likely to make a difference.
As an aside, I raised your point to my friend who works for the Sustainability department - she tells me they put up 10 posters, all of which were recycled after the event.
I think cynicism is often healthy, and it's great to see people questioning and talking about these things. So I'm not having a go - just wanted to contribute my 2 cents about the issue.