I poked around Blogger's feed settings yesterday and found that how much of a posting gets fed is configurable. That is, Blogger will feed all or part of a posting.
This explains a phenomenon I've observed in Google Reader: some blogs' feeds give me complete postings, some don't.
I don't think there is any cost to you, the blogger, if you provide a full feed. You might want to check your blog's settings to see what kind of feed you're providing.