I think the issue is less with the number of tweets per second (not very impressive as you suggest), and instead the requirement that those same 6000 tweets fan

I think the issue is less with the number of tweets per second (not very impressive as you suggest), and instead the requirement that those same 6000 tweets fan out to all of the various feeds/locations that they need to show up at and in a timely manner. If it was a single page with those 6000 tweets/sec it would as you say be entirely unimpressive.