For the texture file itself that is correct. That is not the actual behavior in game though. If the alpha channel is missing then the game will act like it is all white. I have seen this happen myself with some submitted models for my own mod.
Also, I have noticed that (with the NVidia photoshop DDS plugins at least) that if you have an all black alpha channel it basically sees it as not being there as well. You need at least 1 non-black pixel in the alpha channel for the game to properly register it, even if that pixel is in a region that doesn't actually cover any of the viewable texture.