Bethesda has a funny way of celebrating April Fools. Here is the excerpt from The Elder Scrolls website:
04.01.09 - OBLIVION 360 DLC ON SALE (MOST OF IT, ANYWAY)
In celebration of the arrival of April, the wackiness of April Fool’s Day, and the upcoming 3rd anniversary of the release of Horse Armor (Friday, April 3), we are pleased to announce that for the next week (through April 7) all Oblivion DLC for Xbox 360 is half price, except for Horse Armor, which is twice as much as usual.
Nice! So I picked up all the DLC that I didn't already own including Knights of the Nine pack. I had to skip on the Horse Armor this time (I wonder if anyone will bite on the increased price?) but who knows, perhaps when it goes on sale...
Between Oblivion and now Fallout 3 I have spent 160+ hours between the two games. With these DLC purchases and the Shivering Isles expansion, I really have to go back and continue my adventures and gather achievements in the province of Cyrodiil