You can take a general stab at this and claim the perfect storm of Prince Fielder following a playoff birth. Easy to see where the sales have come from. The Prince Fielder signing seems to have been the major catalyst at least considering that they have picked up substantially since we heard on our bookshelf speakers that he signed on the dotted line. Much like the year we picked up Cabrera.
MLive breaks it down a bit here for the last decade. More than I want to delve into anyways. The analysis is somewhat flawed in that it claims the increase in ticket sales is paying for Prince itself, but whatever.
Like I say in every article about MLB and salaries when it comes to Illitch. HE doesn't care so why should you? He wants to win. It's not your money. There is no salary cap. Sacrifice a goat to the goat god so that Illitch can live another 50 years.