Berkshire is a very unusual firm, in that its business is so strongly concentrated within the US compared to most medium-to-big firms. So they aren't exposed to some of the more obvious risks, like a retailer who sells mostly imported goods and therefore either has to immediately raise prices or cut profits.*

The utilities and rails will be fine, depending to a certain extent on the future cost of fuel for both of them. A cyclical economic slowdown always hurts, but cyclical ones come and go. If any part of the hit to the US economy is permanent, that of course is a permanent hit to the companies within it.

But bear in mind that even an insular US firm is affected in a lot of ways. Have a gander at the US dollar index.
stockcharts.com: SharpCharts | StockCharts.com (the level of the USD against a weighted average of trading partners).
If you have a US $100 bill in your drawer, it has only 92.8% of the general purchasing power that it did at the start of the year, and 97.4% of what it had two days ago, no matter where you live. Even if the S&P 500 index value were to be flat today and all of their future reported earnings unchanged as reported in US dollars, everybody holding it is now a few percent poorer in terms of general purpose purchasing power. Which may last, or not.

As previously mentioned, I converted the vast majority of my cash holdings out of US dollars a little while back. At the moment that appears to have been a good move financially speaking.

Jim

* I doubt the market will be flat for this type of firm, Dollar Tree stock is down -12.8% in pre-market trading...