Yeah, how is this obscene? The publishers of those e-texts are the ones giving up income. It isn't a 1-for-1 loss since many of us would not buy all those texts but there has to be some lost income.
You might argue donations to charity should have zero benefit to the donor. That is an ethical decision for every individual to make. I don't feel that way since it stimulates donations. On a similar ethical level is the question of why you are donating to Haitian relief if you know of any hungry homeless people in your own country. Or, if you are American, what you did or did not do for Americans who lost everything due to Hurricane Katrina. I am angered when I see advertising for Hatian animal relief because I know for a fact our local animal shelters need donations (aside from the 'you'll help foreign animals ahead of domestic people?' issue).