Hi, I'm coming from the future.
On 7.4.1 quirks mode still prevails. headers.inl (./iw-cc.war/base/util/headers.inl, ./iw-cc.war/teamsite/util/headers.inl, ./iw-wcmweb.ear/iw-dcf.war/base/util/headers.inl) have a part where if the user agent is IE then it adds <meta http-equiv="X-UA-Compatible" content="IE=5"/>.
In fact the decaltarion for it is splattered all around the place so it's pretty hard to change it.
The doctype declaration is also a factor here but from what I heard from my project lead they got it partially fixed in 7.4.1 (compared to v6).
One nasty consequence on IE8 and 9 of this is that in edit mode the web page edited is in quirks no matter the X-UA-Compatible declaration. This is a performance "feature" in IE as loading multiple versions of the rendering engine posed serious performance issues (as if it would not be slow already).
..and as a warning to any who might try this, lots of the UI (and especially sitepub) does not work at all in IE standards mode, even when you find a way to force it (I've been there).
As fish said, we're kinda stuck dealing with the quirks until HP rebuilds the UI to bring it up to date with current web standards.
We dropped the idea. Even though it's possible, indeed it rains **** on some parts of the UI.