If it isn't, add the keypoint back and add a [citation needed]
Topic on Talk:Dead Island
If you buy the new game, then it's all there, but if you have original version without the DLC you can't buy them seperately anymore, meaning you have to buy the whole GOTY edition to get the DLCs.
http://store.steampowered.com/dlc/91310/
http://steamcommunity.com/app/91310/discussions/search/?q=dlc&gidforum=864943478358422705&include_deleted=1
As the game is pretty old and only places selling regular version are retails and third party key resellers mostly, I guess it should be mentioned under DLC instead.
Tbh, until last week, owner of the original edition had a discount over the definitive edition (it's funny there's now a new level above GOTY).