I cancelled with the same logic you used. I too tried to let them know, but there wasn't a good option in their exit survey, which was actually biased to mask my actual opinion. Instead, I posted to my blog. [1]

So far as no partial refunds, I know their agreement says that, but I saw a partial refund to my credit card within a week of canceling.

1: http://alt-tag.com/blog/archives/2011/09/dear-netflix/