Yes, when you open a file panel or a network browser under Windows, you are using IE. The desktop is IE. The control panel is IE. Friggin' everything is IE! Even if you install another browser, you CANNOT tell those components to use it. So, yes, if you use Windows, you MUST use IE. You have no choice. And must you use Windows? Well, yes. Many web applications aren't written to international standards, they're written to Microsoft-proprietary functionality within IE. This WILL worsen, with this news about IE and Windows 8, just as it worsened considerably after Microsoft violated the Windows 95 injunction by releasing the bundled IE as Windows 98.
I guess you aren't aware but this is all true of Vista and 7. And yet other browsers and OSes exist some how. Just because the Control Panel window is an IE-based window doesn't mean you have to use it to check your email. It's just a window rendered with a web browser. Not that big a deal.
The competition is hurting something chronic. IE has rising usage figures. Firefox is starting to slide. Opera is sliding badly. Chrome may run foul of the Apple vs Google battle-to-the-death. (And one of them WILL die in it, if they don't back off.) Linux has never been fairly or reasonably offered as a desktop choice by anyone other than the OLPC group - and even they are now getting into bed with Microsoft.
Firefox is sliding because of project management (as far as I can tell). Opera has had fairly consistent market share for 10+ years, admirable on some level. I don't think that has anything to do with MS either. The reason I have never gotten into it is the whole built in web server thing. That seems like a really, really bad idea some how. Neither of these things have anything to do with MS. Chrome seems to be doing fine and still improving, I don't see any reason to worry about it. For that matter Safari still comes bundled with all those iTunes installs.
Point is IE doesn't seem that much of a threat to existing browsing technology, it will lose or gain market share based on quality as much as anything.