1. They almost never invest in high technology.
2. They talk about how an unsexy business that produces value for its shareholders is just as good as a sexy one. Money has no memory - money you made from dividends or equity increases in a company that sells bricks is just as good as from a company that sells something more exciting.
Thus, I wonder if a lot of high tech companies are like airlines - people own them because they're sexy, whereas totally decent boring unsexy companies are much lower valued.
That doesn't get into whether Twitter will justify the $10B valuation or not, but interesting to think about - saying Buffet and Munger have done pretty well would be quite the understatement.