No, it is quite true. An anamorphic transfer has more vertical resolution than a letterbox transfer of the same film. Any website will tell you this. If this were not the case, then an anamorphic transfer would have absolutely no visual advantage over an letterbox transfer whatsoever.
It is precisely this extra resolution that was dropped (old solution) or is now downconverted (4 lines to 3 lines) that brings an anamorphic transfer down to a 4x3 letterbox transfer. If you do not believe this to be the case, then please explain why downconversion is necessary in the first place - or do you believe there's no downconversion taking place at all? What, precisely, do you think "Enhanced for Widescreen TV" means?
DVD is certainly a tricky beast to understand.