Building levels to support this new HDR technology was a lot of work. Skyboxes (the extremely large 3D shapes, texture-mapped on the inside, that simulate the sky when in an outdoor level) had to be hand-painted in both normal and HDR-enhanced modes, as well as HDR versions of the standard Source engine cube maps (cube maps are special texture maps, six per object in the shape of a cube, that can be used to accurately simulate reflection on a shiny object). The biggest difficulty Valve found in creating these images was the lack of an HDR-equipped Photoshop. Even the most recent version, CS2, does not support HDR technology. Instead, Photoshop had to be used in conjunction with a third-party image editor called HDR Shop. This was the single biggest gripe that Valve engineers and artists had in the development of HDR content. As Gabe said, 3D video cards already support this in hardware, so why hasn't Adobe gotten around to supporting it in software?
/me cries