That only works as long as the founder or somebody equally powerful is in charge. Everybody else is beholden to the board and thus the short-medium term impact on the share price.

True, but this doesn't invalidate my point. Its more of an argument that non-public or founder-controlled companies enjoy a competitive advantage.

In some cases they can. It will be interesting to see how Dell plays out, even if it's hard to generalize from just one data point.

Amazon is. So is Google. Both have strong founders, and were very explicit in their IPOs about this. Even still, both need a certain level of profitability to sustain themselves. In addition, many companies that spend too much time in the future get complacent about the present. (Look at all the research at Xerox PARC that got commercialized elsewhere)

There are many other companies that either lack that credibility, or have a history of wasting money. (>50% of M&A deals subtract rather than add value to the buyer)