The poll is very black and white "Definitely is; Definitely isn't."
It's all very conditional on your definition of RPG, and seeing as I don't have a clear one, I don't have a clear answer. I'd say it's about as much of an RPG as Metroid is (not very), perhaps a little bit more because your character interacts with other characters more, exposing the world a little bit better.
You get power-ups as time goes on, but the majority of the power-ups are plot requirements. You have no choice about most of them. I'd say the biggest synchronicity it has with RPGs is the quest/subquest model, which you can to some extent choose to ignore or complete.
RPGs are about choices; the more choices you have, the more of an RPG it is.
Final Fantasy is pretty limited in what you can do plot-wise, but it does let you decide character combat roles, progressions, and tends to have fairly elaborate choices you can make in battle. It's basically a more story-oriented version of pokemon as far as I'm concerned. (No I don't care FF came first.)
So on a choices scale, which directly correlates with the RPG-ness of a game:
Adventure Shooter (Halo, storyline and filling a role) --- Action Adventure (w/ Powerups) (Zelda, Metroid: a few choices available, mostly linear story) --- JRPG(FF, [sub]Pokemon[/sub]: more creative combat choices, narrow storyline) --- WRPG (KotOR, Mass Effect: creative progression, some storyline control) --- Pen and Paper RPG (DnD: completely open-ended)
So apparently Zelda lies between Halo and Pokemon.... um....
my chart may need some work.