Nope - still don't get it.
I'm only interested in google.co.uk (pandalized site is a UK consumer e-commerce), so can't comment on US SERPS. Never really watch them. We cancel most orders originating from America because they are too often fraudulent.
Although, I can't say I have been through the data/ done the research for the US, I can't see any reason why Panda itself would be vastly different. After all, it wasn't it described as a roll out to the UK?!
You saying you have a different, rarer (and more fickle) breed of Panda over there?!
FWIW, I suspect not; it's the sample and the population that's different. All anomalies are a function thereof.