It just seems to me that, in a theoretical sense, this statement doesn't really make sense. It just seems that if you have nothing on the hit table except blocks and completely avoided hits, that pushing blocks off the hit table in favor of avoided hits would actually be a good thing. I know we can't actually discuss real numbers regarding itemization on gear that doesn't exist, I was simply responding to a theoretical situation as presented in the manual.
To be fair, he is correct that the particular section he quotes is poorly worded. Point for point, mastery is better than parry or dodge in terms of damage reduction up to the block cap. Having too much dodge or parry is not exactly a problem though. I do agree with emptyrepublic's assessment that having once hit block cap, you should probably funnel excess stats into expertise, but if you wanted to gear entirely for survival you would in theory be fine with continuing to gain dodge or parry past the block cap (this would be assuming you had already changed mastery gems and enchants to stamina where possible). In this case your concern would be to balance dodge and parry as much as possible to minimize your losses to DR. Naturally this is a few tiers of gear away from being possible, if ever at all.