Arioch, true, and a poor choice of wording on my part, between the technical and vernacular use of "parry", I'll use the word "Parry" just in terms of it's RM rules use, and use the word "Deflect" in place of the casual vernacular use of the word "Parry" . . . what you said is the reason the unarmed-unarmored get any parry at all.
Now, the term "Parry" in RM technically applies to how much OB you put into DB and covers the concepts of both evading and stopping attacks.
The person with something they can block or deflect with can:
Block, deflect, dodge or evade
The person without something they can block or deflect with can:
dodge or evade
Hence, a bear can dodge or evade, but it cannot really deflect or block without actually placing part of its body in harm's way. A result of "Bear sticks paw in way and your sword sinks into it 4 inches" is a critical result, not a successful parry. So it takes a 50% penalty to any OB it puts into Parry to reflect that limitation.