Wild speculation: It is the founders that have developed a deep understanding of both computers and people that are likely to be successful. These two domains are very deep and take a long time to learn well (say twenty years at a minimum). Studies suggest that generally people focus on one or the other (men generally focus on understanding things and women focus on understanding people). Find those people who did both at a young age and give them some resources to run a business and they might do very well. As Paul Graham said somewhere, these types of people are only likely to want to start a business as mundane as "make file backups really easy and reliable" if they will be very successful and that success will let them hang out and work with similar people.