Wow, really? I thought 2012 was very much anticipated? I know a lot of people are using satellites to take FTA feed from Germany, RTL, and then use BBC radio 5 live commentary for commentary. I guess a fair amount of people might have seen it via that or other methods that don't include Sky or BBC (or internet Sky feeds).
With 6 world champions, very close mid field cars and a very good chance of a Brit winning the world title, it could be a vintage F1 season, so the figures are not good. Like you said though, I also know some people using RTL and R5 to watch it.
If you put the BBC figures in isolation so compare the race figures, 2.73m (2011) with 2.85m (2012) and qualifying , 2.06m (2011) and 2.02m (2012), then they will be pleased. If you put the Sky figures in isolation so compare 617k with their own estimates and other sports figures, then they will be pleased.
But if you bring them together, and compare the peak viewing figures with previous years, then the figures are down by 24%, which is disappointing. The two broadcasters' will probably be pleased, but the combined figures are not pleasing.