there has been a huge amount of money thrown at studying how to get people to spend money, and using .99 is effective. It's not scummy. It works. Companies wouldn't do it so much otherwise.
Hilarious, if you think manipulating people in order to get them to pay you more money is not scummy then you're a fool. Companies usually couldn't care less if they're tricking the person into buying their product that's why they have marketing people. Farmville is the perfect example, their goal is to farm the player's money as much as possible. "I'm not going to treat you as a normal human being because I know I'll make more money off you this way".
I guess it comes down to an issue of respect, do you respect your players as intelligent people? Or do you just view them as a money resource who you should manipulate so you can make profits from them?