The difference being with Python you gained in prototyping speed but were losing (at least at the time) on execution speed, whereas in D you get rapid prototyping while keeping very high efficiency.
Good point. But that is partly due to the design of Python, it being a highly dynamic language. I don't want to get into any flame wars, but I'd hazard a guess that Python is somewhat more dynamic in nature than D (I know some D, and Python well), and that at the least, some of the things one can do in Python, would require a lot more knowledge and skill (with D) and acrobatics or contortions (speaking loosely) to do in D. (It would be good to be proven wrong on this, though :) This is not a criticism of D, I really like the language, and am aware of its power. Check out these two posts about D by Dmitry Popov (lead developer and Director), on the Infognition blog:
In fact, here are some posts I've written that show how to write some kinds of basic apps for various purposes in D, that I posted about on HN just recently: