Have been thinking about this for a while.. The answer that follows is based on insights I got from a panel in SF and from discussions with my co-founder Rob Attwell. So why is Silicon Valley/SF the birthplace of most great tech companies? It's about the unique concentration of 5 Cs:
1. Coders (esp with experience)
2. Concepts (new ways of solving things that end up in SV/SF because everywhere else they are deemed crazy)
3. Customers (willing to try things and with disposable income)
4. Cash (investment)
5. Competition (essential to keep you going faster and higher)
Lots of companies there have grown too large or not provided enough internal growth roads for employees to retain top talent over time. Start small, get really epically large then hemorrhage top talent into the local ecosystem. If you're an NPR fan there's a whole This American Life on why Chicago needs to have a Groupon type of firm get all big and uncool to work for so that the local economy spawns more innovation.