You are thinking right. What would stop all the major brands to go out there and buy the "spammiest" links networks pointing to their competition. How does the competition prove they did not do it.
I think Google dealt with this years ago with the Miserable failure change.... here. They basically altered their algorithm to not give "too much" advantage of links/anchor text from all over the web. In a sense, they created the ability for their algorithm to discount the value of links, not penalize the website being linked to. Does that make sense ? I think what's happening now is not any different...they can and will continue to identify link spam, de-index link networks and manipulative techniques using pattern identification. But if not all, most cases, discount the value of those links...and not directly or not 100% penalize the site being linked to, because then technically a group of people/websites could run a mass campaign and kill any online business. That's not how the Internet is supposed to work...