In the context of what I was saying, challenge maps are a copout from adding new content; i.e. branching story or different perspective ala Half-Life Opposing Force/Blueshift. Honestly don't care how common they are it's just a quicker release. It's more of a moneyplay for people who just buy dlc site unseen. There are people who just want to mash buttons and there are people who want to be entertained and/or learn something along the way.
Just because DLC focuses on gameplay rather than story doesn't make it inherently bad. The map pack for Mirror's Edge was great. Comparing new levels to horse armor is ridiculous, as maps take significantly longer to create than armor.