jonnythan:
Because it doesn't matter. When someone says "my octopus," everyone knows what that person is talking about.
It does nothing whatsoever for the industry to change the common meaning of the term octopus and forcing a new definition for it would cause nothing but problems and confusion.
The *only* reasons to insist on this definition is because you think it makes more sense or because that's where the term originated. But it doesn't matter. It means what it means and everyone gets it.
I can get as pedantic about language as anyone alive*, but I must strongly agree with you on this one. In real life, usage determines meaning. It's as simple as that.
*here are some examples:
The past tense of "to dive" is not "dove" (that's a bird). It's "dived." The past participle is also "dived." People get confused with "drive" (drive, drove, driven) and want to use "dove" as the past tense. If they kept the past participle in mind (nobody says "If I had diven with the correct equipment, the dive would have been more fun") then there would be less confusion. I will bow to usagists about this one (everyone I know says "dove") but will continue to use the correct term in my own speech.
The plural of "octopus" is NOT "octopi." That reflects a poor understanding of etymology, since octopus is not a Latin second declension noun at all (singular -us, plural -i). It's Latin stolen from the Greek oktopo(u)s in which the "pus" (the plural of which is "pedes") refers to foot. The most correct plural is "octopedes," but in English "octopuses" works best. The name of the order is the Octopoda (still not octopi). I usually say "octopuses" and get looked at funny, especially by those who know I speak Latin and think I've undergone a brain fart. Everyone I know says "octopi."
http://itre.cis.upenn.edu/~myl/languagelog/archives/000813.html
Even if you only have one arm (which is the body part between the shoulder and elbow. The bit from elbow to wrist is the forearm), you still have "a biceps." There's no such thing as "a bicep." I will not budge on this.
Medical diagnostic terms such as "schizophrenic," "psychopathic," and the like have specific technical meanings, and one may not simply co-opt them for use when one wishes to lend an air of authority to one's insults or other pronouncements. (It's likely best not to get me started on the distinctions among schizophrenic, schizophreniform, schizoaffective, schizotypal, and schizoid.)
And on and on and on... (See, I'm flexible! I began a sentence with a preposition!)