Interesting... Google Earth is using .dae too. For my ETQW map I imported a .dae model of a real building, manually fixed it (most of the faces have been broken but the vertices have been ok so I had to rebuild them), then I exported it to the ETQW editor via .obj and rebuilt it with brushes to be able to hollow it. I did it to get the proportions right...
... pure speculation but if CryEngine 3 is using .dae then maybe the base for the buildings in Crysis 2 have been ripped Google Earth models?