It would be interesting to see the same graph but with other computer / electronic appliances of the same price range. I have a feeling that people who bought the iPad didn't feel like splurging on other items as well. The iPad is definitely a discretionary item, and people tend not to buy too many of these at the same time in the current economy.
So yeah, I think it's quite possible netbook sales got indirectly cannibalised by the iPad, and I have a feeling that other discretionary items of the same price range were hit too. Well, that's my opinion. You can't prove these things either way, unless someone went to survey iPad users directly: "Were you going to buy a netbook instead, if the iPad did not exist?"
So yeah, I think it's quite possible netbook sales got indirectly cannibalised by the iPad, and I have a feeling that other discretionary items of the same price range were hit too. Well, that's my opinion. You can't prove these things either way, unless someone went to survey iPad users directly: "Were you going to buy a netbook instead, if the iPad did not exist?"