Why Is Printer Ink So Expensive?

I've thought about this every time the dang printer runs out of ink. Why is it the ink ends up costing waaaaay more than the printer? It really bugs the heck out of me that I had to hack my Brother 240C printer to print black just because one of the colour cartridges dried out.

From Boing Boing, a graph that compares the price of inkjet ink to other liquids. Hint: Ink costs more than human blood. Way more.

From the comments, one possible explanation:

Genuine HP Black Ink #45 is made by washing Karl Rove's soul in the tears of unicorns, for maximum opacity and colorfastness. Cheap 3rd party cartridges just aren't the same.