I spotted a similar comment on one of CNN or MSNBC's website about this phenomenon. More or less, the issue is that startups are looking for innovation and at least a point of difference from the competition. Once a startup has its IPO, the corporate culture tends to turn from innovation to "shareholder value". A.K.A.: make more money. Attempting to make more money doesn't preclude innovation, but often there is a subtle ossification around what the company is willing to spend money on if the board of directors isn't headed by visionaries.