Somebody might come along. And they might not. The point is you don't have to create an exchange rate. It's not needed. When people do that they do it because they don't know what the hell they're doing. As I said, if you don't know what the hell you're doing, don't use story points.

You might as well estimate in domain-specific terms

Actually no. You could use your astrology chart to estimate, but the purpose here is to get better and better as you go along. Remember that we re-estimate each sprint (or at least we should). So the point is the informal model of execution evolves over time. The old way was constructing this huge model and spending maybe 20 hours creating the perfect estimate, then executing. The new way is spending 2 hours each sprint over 10 sprints, increasing accuracy each time. You want a simple, less complex model that can be rapidly iterated. Lots of little bad guesses converging on an answer based on real-world execution data.

This is getting much longer than a HN thread. I would caution you that things like COCOMO exist as a way to mathematically model how time interacts with development. It's a model, not an explanation. Don't confuse tweaking numbers in a spreadsheet with controlling or changing execution. Various models have various uses. Technology development does not break down in a scientific management kind of way. Yes you can decompose technical problems into tiny pieces and solve them. But people working together are not robots, and their work cannot be broken down in the same fashion as a algorithm can. Wish I had time to go into this. Check out this blog entry. http://tiny-giant-books.com/blog/agile-backlogs-sigh/

Thanks for the chat!