I'm actually writing another (long) post on exponential growth and the different phenomena that could lead to it. Multiplicative costs are on the list of plausible explanations. I've discussed these multiplicative stories with Jonah and Luke before.

I think that multiplicative costs is a major part of the story for the exponential-ish improvements in linear programming algorithms, as far as I could make out based on a reading of this paper: http://web.njit.edu/~bxd1947/OR_za_Anu/linprog_history.pdf

More in my upcoming post :).

UPDATE: Here's the post: http://lesswrong.com/lw/k1s/stories_for_exponential_growth/