I don't have an answer, but the question is not really stupid either. I think as far as the info sections are concerned, 2008 and earlier products no longer exist. It seems that way for the civil stuff anyway. For your purposes, I think the 2009 information should be roughly the same for 2008 except in the areas affected by the core application. Things like "Ribbon" will change the interface some, but since you can ditch it for the classic menu there should be documentation flags for those. The basic Arch Desktop functions should not have changed significantly, but some things may work better and others may be broken.