Mind you, the trams there do have air conditioning you can actually feel, as opposed to the pitifully weak effort on Melbourne's trams/trains (presumably adjusted down to the bare minimum to cut the privatised operators' electricity costs). Perhaps that's what the ad revenue pays for?
Sydney's buses also have video screens, which today were displaying Fun Facts About Christmas (i.e., about reindeer and Christmas trees and such, not about Jesus Christ or Mithras or the like). Not sure what the point of those is; perhaps they'll gradually sneak in ads?
(Yes, I'm in Sydney right now; I'm typing this from Peter's house. I've been on the road since Sunday, hence the recent sparsity of blogging.)