Seems odd that a simple, reasonable model would be overlooked for decades. Maybe other investigators just never felt the pressure-free fluid model seemed likely to be the actual way things worked. Maybe people have been scared off by the relativity equations. These guys must be thrilled.
Edit: I skimmed the article. Very interesting. We'll see how this plays out. I'm looking forward to the LHC results. Maybe they will reveal supersymmetric WIMPS.