I'm just pointing out that your logic is faulty, because you imply that the sheer size or valuation of the company should be sufficient to assume that the general public, or at least the audience, knows about it so that providing background information on it is unnecessary. We wouldn't do this with Cargill.
Now if you had said that, because of Slashdot's userbase and its technical/computing background, it's safe to assume that readers here are sufficiently familiar with Microsoft to make background information unnecessary, I would completely agree. But I would also say the same for Mozilla, which is a much, much smaller and less valuable company than MS. Same goes for Wikimedia Foundation, the FSF, Newegg.com, etc. Background info on those companies (or non-profit foundations) are not necessary here. Company size and valuation really isn't important, it's the audience of this site and the nature of the company in question.