Related work is motivation. It's part of the story.
It depends on the paper -- in many cases, I think that a paper can be adequately motivated in the introduction, without explicitly enumerating all the potential related work. Given that most people stop reading quite early into a paper, I think there's a lot to be said for getting to the "Good Stuff" quickly -- and the related work is rarely the "Good Stuff".
Perhaps related work is more important for incremental, technical results: "problem A is important, B and C tried to solve it but their solutions were imperfect for reasons D and E, and therefore we propose F." But when you're, say, describing a new piece of systems software, the related work is less likely to be an essential part of the motivation for the paper.
It depends on the paper -- in many cases, I think that a paper can be adequately motivated in the introduction, without explicitly enumerating all the potential related work. Given that most people stop reading quite early into a paper, I think there's a lot to be said for getting to the "Good Stuff" quickly -- and the related work is rarely the "Good Stuff".
Perhaps related work is more important for incremental, technical results: "problem A is important, B and C tried to solve it but their solutions were imperfect for reasons D and E, and therefore we propose F." But when you're, say, describing a new piece of systems software, the related work is less likely to be an essential part of the motivation for the paper.