I've been digging around on this.
Elements3 (for Windows) introduced a new Organiser tool, which it integrated with the Photoshop Editing Tool (cut down version from the Photoshop codebase). This Organiser was built into Elements itself. Elements4 (for Windows) still maintains this system. This is what the original poster was talking about. I agree with him that its a very nice system once you get used to it.
Elements3 (for non-Intel Mac) introduced the same Photoshop Editing Tools (again same Photoshop codebase), but did not include the Organiser tool that Windows had.
Elements4 (for non-Intel Mac) came out a while after the Windows Version. Again, this version does not have the same Organiser tool that Windows version has, built into it, as the Mac development stream is seperate from the Windows one when it comes to Elements.
HOWEVER, what they did do was include a cut-down version of Adobe Bridge (Bridge is the management tool that comes with full Photoshop).
It seems that Bridge has some extra stuff in it compared to iPhoto. However, it doesn't seem to integrated fully into Elements4 and it works in a slightly difference way to Organiser in the Windows version.
There's some stuff about it over here.
http://www.macworld.com/2006/02/firstlooks/elements4/index.php
http://www.oreillynet.com/pub/a/mac/2006/05/16/photoshop-elements4.html?page=1
Another thing to note. Elements4 is not a Universal Binary.
From what it seems iPhoto is pretty much there when it comes to photo management... but I would like to have a nice photo editor. Hmmm. May have to take a look at GIMP or whatever it's called.
... and what I really need is good RAW support.