The issue with weighting is that some group is always going to feel slighted or undervalued. I can't understand why (it's just a number). But benny1967's explains the issues I could think of with having them combined.

But by having seperate counts, at least for distributing prototype devices Nokia could split them between developers [for building applications ahead of time] and the community [bug finding, reviews, critiques, handling the masses, etc..] if there were two different "karma" systems.