[icebraining]

You are being deprived of something you never had. If someone says they'll gift me a car, and then they don't, have they stole from me? No, because I never had the car in the first place.

And who's to say you are being deprived of such income? For all you know, you could have received the exact same amount even if the pirate publisher had never sold it - maybe he did all the marketing work that enabled those sales.

More: for all you know, maybe the marketing work that the pirate went through has helped sell more of your publisher's copies that it would had the pirate never copied it at all.

It's simply impossible to tell if you were deprived of any 'potential income' or not.