Is it only because the time it takes other fields to adapt to new methodology is longer - or are there other factors?
EDIT: Holy crap, I worded this terribly.
Rewritten: Why does going across domains with new ideas have such high returns? Obviously you're a fresh idea but are there other reasons that influence your success?
Basicly I think its because they have different points of view on problems we can find similarities in.
Perlis, epigram 39: "Re graphics: A picture is worth 10K words - but only those to describe the picture. Hardly any sets of 10K words can be adequately described with pictures."
There are worlds of esoteric knowledge stuffed away in industries that, if applied to other industries would yield amazing innovation.
Look what Apple has done with Technology/Liberal Arts.
Apple took technology, created by developers and scientists ('Nerds' for lack of a better generalism) and not only made it accessible; they made things work the way people wanted to use them. Desktop publishing, graphic design, etc. These were things that normal people would not have been able to easily use without a GUI and the tools in place for the creation of the software.
If you think this is a natural progression of computing, you're really not giving credit properly.
Look how much UX has improved since Google started their redesign initiative. We can sit around an nitpick about whether its good or bad; regardless, its easier to use! Its easier to understand than it used to be! Improvement!
When it comes to applying knowledge across domains, its almost a corallary to the Observer principle (if you'll allow me some metaphorical license). The more accurately you are able to observe a specific detail about a larger system, your observations about other details in that system will be less accurate. If you approach a problem, design or otherwise, with many observational vantages; you're less likely to miss details globally.
Did I talk myself into a hole here?
See also: mbarnett's response. I can't say it better than that.
As I was once told: "the problem with being a tenured prof in a multidisciplinary department is you have to do tenure-worth work for both sides"
There's a theory / definition of creativity that says that it's simply the ability to connect seemingly unrelated things. This is an example of that.
Hamming suggested it, "You need to get into a new field to get new viewpoints, and /before/ you use up all the old ones."