I think part of this may be that since programmers typically make more money and tend to be more valued, the upside for them of doing spec work is much higher.

I think part of this may be that since programmers typically make more money and tend to be more valued, the upside for them of doing spec work is much higher. Even if salaries for developers and designers are comparable in startups, this is in-general not true from what I've seen, so designers as a community have banded together to stigmatize doing spec work. I'm explaining this situation, and how I think we might have gotten into it. To paraphrase a W3C spec: this comment is not normative.