I went in today to sign up. At first the salesperson said that I had to purchase a tv or something else (I didn't ask what) in order to get the deal. He had shown me a brochure and nowhere on there or on their website did it say 'purchase required', which I told him. After some discussion with another person, he said that yes, I can get the free install and he took my details.
(I've saved a pic of the website just in case they decide to change it to purchase required.)
I've received a confirmation email from Sky with a bit more detail, but pretty much saying what is on the Harvey Norman website. I'll get a call within 5 working days to get an appointment set up.
So if you've been thinking of getting mysky, now's a good time!