Cartman takes one of the stars above the middle hump on the back of the sofa, but the one shown missing soon after is the one to the left.
Some of the "damned" characters in Hell are clearly not evil, just dead. For instance, Michael Landon, Princess Diana, JFK & Jr., and Gene Siskell. While they are not evil, it was probably the series' creators' way of paying tribute to those who had recently died, and in the case of those long deceased, like Landon and JFK, they were noted for marriage infidelity, which is considered a sin.
In the song "Christmastime in Hell," Hitler opens his gift from Satan and exclaims, "Un Tannenbaum!" Hitler spoke German, so he would have said "Ein Tannenbaum!" Satan even replies with the same wrong phrase.