<<Could it be that the other browser render web-pages like they should be rendered according to W3C-standard, while IE does not?>>
Good Point! and to prove that-
I know that when I design a page, I check 'em in every browser and platform availble to me (4 computers in my house helps a lot!).
I gotta say Opera, or Mozilla seem to render a lot more 'true' to the code that my poor little fingers type out in notepad!
I make something in Front Page, and it renders beautifully in IE, but not quite right in other browsers. hmmm.......
I remember thinking that the Web Browser was awesome, but wouldn't last, BOY I WAS WRONG!

I used the MOSAIC Browser when it first came out (on my Mac Plus 6" B&W Screen)! I used IE until 4, I just had bad luck with the IE4.x versions (on the PC).
Used Netscape and Mozilla durng the IE4x days, didn't necessarily like Nutscrape, but it worked.
I Think IE5.x Versions are great. Java's real nice. So happy with it i'm afraid to go up to 6.
Opera 5 is great too. Tried 6, and though it was kinda weird.
On the Mac Side, I use either Netscape 4.7, or Mozilla. Honestly haven't tried IE5.x yet, but 4.5 was, clunky, slow, crashable, and a headache.