Maybe big, financed brands get a pass because they can afford fancy lawyers and google doesn't want the headache.
I have seen pieces of this traffic behavior on at least one very big, well financed brand. However, it was for a very hotly contested keyword, and there are more than ten big brands who want to rank for it.
The implications of traffic throttling, if it is really happening as it seems to be, are immense. But I think all the guessing and theorizing won't get us very far. It hasn't in the many years that people have been noticing "something strange". And I don't have such a site under my care right now - or I would be digging like crazy to find out what the devil this phenomenon is.
If we can establish what is going on (and it might be more than one "thing") then we'll see where we can go with it. I'd particularly like to focus on the fact that traffic for some sites seems to be level across all entry pages - rather than just of one page or one keyword. If Google is intentionally creating such a limit or traffic cap, then that is a very big deal.
Several members have shared some of their data with us - and that's what we need if we're going to understand this.
[edited by: tedster at 3:55 am (utc) on Sep 21, 2010]