I haven't been a member here long enough, nor do I know the locations of everyone well enough, to say whether or not this is something perpetrated mainly by Americans, but I'll assume that it IS just because that is what the topic was about.
If quote misrepresentation is done mainly by Americans, here is my theory as to why:
We all know in American politics it is a two party system. One effect of both the two party system and the abundance of interest groups is everything is taken to extremes. You are either PRO LIFE or PRO CHOICE. You are either PRO WAR or ANTI WAR. You are either PRO GAY MARRIAGE or ANTI GAY MARRIAGE. You get the idea, and I'm sure you've all seen this. Because the ideologies of both political partys are so based in money and partisan garbage, everything has to be black or white, there is no grey area.
These extreme way of thinking will trickle down into the CFC population, because we tend to be politically aware. So even when a topic is created about something other then politics, it shifts into extremes (you are either a religious nutbag biblical literalist or an anti-religion atheist god hating wierdo).
Since every viewpoint is shifted into extremes, every quote will be shifted accordingly. In the example posted at the beginning of the thread, you are either FOR military spending, or AGAINST military spending.
It is as if every argument was a mountain, and every opinion was a boulder. even if you place your boulder just a tiny bit to one side of the mountain peak (the peak being completely neutral on the subject), it will roll down to either the far right or far left side of the mountain, whether you like it or not.
That's just my thoughts as to why
I don't think its as much a conscious decision as some have said, its a subconscious effect of the tendancy to lump everything into black or white extremes.