Umm... you can't buy an indulgence. Even the NY Times got that part right. I understand it much like Bluegoat was talking about. When we work to purify ourselves here on Earth, it purifies us. The idea of praying for the dead (including seeking indulgences for the dead) does have a Biblical foundation (at least in the Catholic Bible). 2 Maccabees 12:38-46 tells the story of how the people who were killed in a battle had amulets to an idol and how those still alive gathered money for an offering (In this case, it was even monetary.) and prayed to atone for the sins of the fallen.
It is also about the communion of saints. It's similar to the idea that we can offer up our sufferings for each other, that Jesus suffered to give us a gift that we couldn't really have earned on our own: heaven.
Indulgences are not what we learned they were in high school history class. I was taught in school that there used to be a widespread practice of selling indulgences. I was also taught that sins were assigned a certain number of "man-hours" or prayers, so if a king or someone else rich wanted to sin, he could just pay monasteries to pray and go ahead and sin as much as he wanted. I don't know how widespread these practices were, but I doubt that they did much to get people into heaven. I believe a change of heart is needed for that.
As they are practiced now (and probably how they were originally intended to be practiced), indulgences are designated acts that, when practiced with a pure mind and heart and combined with confession (I don't know if there are any that don't require confession), fulfill the purification requirement that would otherwise need to be completed after death. Spero, if Purgatory is a state of being that can be reached on Earth, then an indulgence would be a practice that puts us in that state of being now. Since most of us don't die perfect, I still believe that we can go through Purgatory (as a place or state of being) after death to purify ourselves of any sins that we still have on our souls at the time of our death.