Your answers makes it more clear. Yet a couple of questions remains. How can the case of english in USA, or latin in western europe be similar to PIE? Those two are conveyed by One single civilisation or empire. the whole area is influence by one culture. Was there such a Proto-indo-european empire reigning over an area as vast as the whole indo european area? I think it is hard to believe without a writing system or a more or less advanced technology, which is important for maintaining coherence on such a big area for a long time. I do not doubt some comunities had the colonial and dominating style at that time to, i just think their influence was restricted to smaller areas.

        If the langage did not have the support of such a big civilisation how could it manage to replace allmost everything around? And it seems that if it is just spreading around, without any control, by the time it reaches areas quite distant from the original location, there could hardly be anything left from the original language.
And how can there be only one "winner" on such a wide area? Wouldn't it be more reasonable to think that this reconstructed root comes from one proto-indo-european language, and that other comes from a distinc language, potentialy non related?

        As for the number of language in the early world, i agree partly with what you say. Now adays, the world's population is around 6 bilions, with more or less (i believe) 3000 languages. that is an average 2 milion speakers per language. and if you consider only the "major" languages that are likely to survive in the future, the you get an much higher average number of speakers.

        At the time when the world only had, let's say 10 milion inhabitant, it was a rather prehistoric world. the prehistoric civilisation nowadays have around 1 language for  thousand people. So that still makes 10 thousands languages. This is purely hipotethic, and rather simply calculated, but i think i gives a routh idea. I guess you have to get back much farther in time to find a moment when the number of languages decreases. I am not even sure this time exist, because there is no way to know at when people started to talk, and how wide spread mankind was at this time.

        Just as a final word, i want to make one thing clear. I am not stating that i am right and every body else in the world is wrong. I am just giving my view so other can comment on it and tell me where i got wrong. And i hope not every thing is wrong ;)