I'd take that with a grain of salt. Valve may have implemented a nonhierarchical company structure but there are always going to be big dogs and little dogs regardless.
Plus, there was some news recently that they shut down their hardware department, where I think they were working on holographic projection. The most likely reason for this is that hardware requires a pragmatic approach, not a creative one, and in their flat company there was no room for people whose only function is to do the dirty work. Grunts, so to say. That was not an option, so away went the hardware lab.