That is an interesting theory about Oprah. As much as we all like to feel like we know her and who she is, we have to admit that we don't. We don't know her at all. All we know is the personality she portrays in public. Celebrities and the image they portray are pretty much a combination of who they are naturally and who their publicists, makeup artists, agents, so on and so forth create for the target audience. Take Martha Stewart - she's actually a loony toon, and Eddie Murphy is said to be one of the most dull boring people you could meet in real life.
So, if we admit that Oprah is a celebrity and therefore subject to the same image-creating they all are subject to, then it is possible. I'm not making accusations, just saying that celebrities do go to vast lengths to maintain their audience, and packing on a few pounds to make her more relatable to her female audience isn't really all that crazy.
People tend to think of her as somehow special and different, as if all she does is truly just out of the kindness of her heart. But, it is her job to get on that stage and nod in her understanding way with a couple of tears, and hug the guests, donate money appropriately, and so on. That is her image - the "I know how you feel" talk show host - and struggling with weight goes right along with it. So, while I'm not accusing, it does make sense. As much as she is practically worshipped among housewives everywhere, she is a media created celebrity, just like the rest of them.
Please don't shoot me.