Not everyone cares to use IE. And while Mozilla may not be perfect, some people prefer that. No changing their mind. And many are to the point that if you can't bother to make a page that is standard, then they'll not bother to visit. Not trying to be mean, but it's true.
This is very true, while I could use IE, I refuse to, as Mozilla is my (compliant!) browser of choice, if i was using Linux/BSD I wouldn't have the option of IE at all.
This is why more sites need to be compliant. A compliant site can be viewed in any browser.
errr, wtf is an IE stylesheet?
CSS stylesheets follow a set or regulations set by w3, any compliant and valid sheet will be read perfectly by Mozilla, because it's a compliant browser. The same goes for any (x)HTML code.
Personally, I don't even think it's about being compliant. Any decent website should be at least renderable in any browser.
NTFS.org is a good example. Sure that "logo bar" on top don't line up correctly on the main page, but at least I can see it and I can see the intended effect. But when a site "requires" a particular browser and don't even load at all, I think there's a problem.
It's not about standards to me, it's about me being able to choose what program I use for what. It's not my lose that your page isn't viewable to me.
Even the Microsoft.com website is usable in Mozilla.