[peterwwillis]

Having both good leadership and good engineers is more likely to provide success than just good leadership. That said, having only good engineers without good leadership will lead to failure. But the companies you mention require different amounts of net engineering effort to achieve their respective goals.

Hiring the best engineers doesn't seem to be as big a factor for companies like Facebook, for example. Facebook found means to connect people in ways that kept them engaged with the site, which was more of a social programming [psychology] problem, which while still an interesting engineering project (from a web-design standpoint) is more of a question of designing features people want to use.

Google wanted to provide more relevant search results, and so engineering was a key component in solving a complex problem. DropBox was similar in that they were providing a way to reduce friction in a basic user experience: synchronizing file copies. But DropBox's solution is nearly all engineering, because the problem they're solving is almost entirely based on managing logical resources (which is something engineering is great at).

However, if you leverage technology poorly, your company will suffer. Myspace ended up developing quicker with less engineers in Coldfusion than Friendster's greater number of engineers using JSP. Years later, Facebook gained great success using php - but was it because they used php, or because the goals they were focused on were different, or their execution more deliberate?