You know in T.V shows, that they filter out brand names, even McDonalds? I couldn't understand why they'd do that.
A novel is not a TV show. If you want to write novels, you need to read novels, not watch TV.
One of the many differences is the business model. TV shows are paid for by advertisements, not by individual viewers. This works because TV shows are typically seen by millions of viewers. Besides commercials, businesses are also willing to pay for their products to be seen as part of the show. That's called product placement. On reality shows, sometimes a brand name product gets into a shot by chance. Those products are blurred out to avoid giving away free advertising.
Novels, outside of rare mega-bestsellers, are lucky to be seen by a few tens of thousands of readers. That's one of the reasons the advertising model of funding isn't used in the publishing industry. Anyway, I think most people would regard it as selling out. The good news is, since advertising isn't an issue, the writer is legally allowed to mention any brand name he or she wants, as long as it isn't in a negative or damaging way. However, just because it's legal doesn't mean it's a good idea. The question becomes whether mentioning a brand name will enhance your novel, or hurt it. The answer depends on a number of factors that are different for every novel.
In your particular case, one big issue is whether it's believable that your fantasy world is so identical to the real world that the same companies created the same products and achieved the same level of success by beating out their same competitors. None of us can answer that for you; we can only suggest that you think about it.
Fantasy stories have been done with the premise that they are set in the real world, that the fantasy elements really do exist, but most people just aren't aware of them. It could be that's how your story works. If so, fine. No one is saying you absolutely can't use brand names; we're just asking whether you've thought it through.
Of course, then you get into the issue of how to handle brand names well. Doing it badly can annoy readers. There are several threads up in Writing Novels, or maybe in Basic Writing Questions, where that is discussed in depth.
