that makes sense- except it only runs on a windows OS anyway- (old mac versions aside)- firefox runs on almost all popular platforms.
Since the IE install is part of windows and it only runs on windows, it is essentially free since you would need to buy windows even if it was a separate product.
As an example, if office was included, would we not call it free simply because of that?
Or; we could be talking about the WGA cruft they insist on performing when you attempt to download IE7 for example; unfortunately for them, a quick google-search finds many un-WGA required downloads of IE7. (not the latest version sometimes, but it's a workable solution)
Not that I even touch IE voluntarily anymore.