I wouldn't stress about it. Just get name brand non -conductive paste like MX-4 or use whatever came with your cooler. Be Quiet, Zalman, Noctua, Arctic, or whatever. You could rank them if you did enough research but they all will work fine. Most important is the application and a smooth install of the heatsink.
More to your question, I think it's probably marketing. Next we'll have someone marketing titanium once gold is old news.