While it would admittedly be easier if all this community stuff was part of the Netflix site such that your nickname and avatar from over there would automatically present themselves over here... the next best thing is that it would make the community easier to follow if you used the same image and name over there and here. That way there is at least a little logical continuity.
It's not a rule, of course. Just a suggestion.
(I've clicked on a few of you and saw your Netflix Profile page and went "ohhhh, it's HIM....")
What if the default purple avatar looks like you? I am: a pensive brunette who occasionally twirls a lock of hair about her finger as she ponders the grammar in her reviews.
One of my favorite Netflix reviewers is Blanche, who uses the Simpsonian avatar -- I don't think the less of her for not having a picture of herself or her favorite pet.