October 23, 2017, 4:00 pm EST

Forbes has just ranked the top 400 richest people in America for 2017.

Among the top 50, a fifth have created their wealth from some sort of Wall Street activity (mostly hedge funds, but also brokerage and asset management). There’s not much new there–the rich have gotten richer on Wall Street despite the challenges of the past decade. But as we’ve discussed, the torch was, in many respects, passed to Silicon Valley over the past decade, as the best spot to create–that’s where the biggest proportion of the wealthiest 50 have built their wealth.

But much of that technology wealth can be refined down to the very industries that are being displaced on the wealth list, such as publishing, energy and retail.

That makes you wonder how long some of these companies can command a software-like valuation when the core of their business models are rather traditional things like selling ads, distributing content, making cars or selling retail products.

To this point, as long as they started in Silicon Valley, they tend to get a very long leash. They can lose money with immunity.

Consider this: GM is valued at $66 billion. Telsa is valued at $57 billion. GM has made (net profit) $43 billion over the past six years. Tesla has lost$2.5 billion over the past six years. Meanwhile, Elon Musk, Tesla’s founder, has amassed a $20 billion net worth.

The question is how defensible are these businesses (Facebook, Netflix, Tesla, Twitter)? How wide is their moat? A couple of years ago, the answer was probably very wide–very defensible given the adoption, the scale, and the deep pocket investors that were willing to continue plowing money into them. But, as we’ve discussed, if the regulatory environment becomes less favorable and the money dries up (in the case of private companies, like Uber), the operating advantages can begin to evaporate. This bubble-up of regulatory scrutiny on tech is something to keep a close eye on. It may become one of the big themes in the coming year.