Are IE6 and IE7 Standalone Browsers The Real Thing?

Today I finally got around to making Windows XP images to have all the versions of IE running for real. And then I compared them to the "standalone" versions and found no difference. Ever. Even on the strangest IE6 rendering.

So I asked for evidence of the "you can't have more than one real IE running at a time" position on SO. As expected, the question got little interest and no new data points. What did I expect? Hearsay is cheap, and evidence is hard to come by. The standalone IEs (not that IETester thing) are perfect, in my experience, and when they're not, it's that I got confused in my testing. I haven't been able to find any differences.

1. IE6 in MultipleIEs install.
2. IE7 Standalone.
3. Then install IE8 for real (as in download it from Microsoft).

Three IEs on one XP box isn't bad. 

And browsershots ain't bad either. Litmus, on the other hand, seems like a cheesy simulator, in my two days of experience with it... but that might be wrong. Anyway, I don't care what the site looks like on a bunch of browsers. It's a UI: it's a question of look, feel and behavior. That's something screenshots can't tell you. That's why I need these browsers to take up as few virtual machines as possible, hence the initial question.