Perhaps the PC version was not expected to do well and hence not receive any DLC, so nothing was built in to protect DLC from easy and immediate piracy. How do you protect a single data file from being freely copied from one machine to another without rewriting a huge chunk of code that ultimately would not pay for itself. Consoles need no such protection as the console itself is the protection and this reworking of the core would be for the PC version only - the PC version that was expected to do poorly to begin with. It's unfortunate that the PC market share is in that state right now, but it is and the backlash and bitching won't help to change that. What will is buying the games and voting with your money. Yes DRM is bad, but nothing to buy is worse. Companies expect flak from DRM, expect everyone who writes that flak is a pirate, and they don't read your posts - they read sales sheets. Some web jockey gets to distill the crap from the water and present it in bullet form for exec's to ignore later.
Despite the forums, the DLC is on Steam's Top Seller's List at #2 at the moment and while many bought it without knowing about the protection, what this shows is that 2K/Gearbox was wrong. PC gamers do buy PC games, do want DLC and, according to the forums, do want to be treated like honest customers. Next time take a page from Borderlands and expect that people will buy your product, even on the PC!
For those still sore, the DRM was most likely put in place as a temporary fix until the patch arrives. At which point, thanks to the buyers of the DLC, it will likely be removed and replaced with a proper solution so they can sell us some more DLC.
EDIT: A De-Authorization Tool has been released.
