Berlin isn't a great place to hire developers:

1) Employees get lots more legal rights in Germany compared to the US. I don't know if this is the case among startups but certainly at larger german companies I've seen the programmers are unionized. So when you don't get that next round of funding and are forced to reduce headcount you'll pretty much have to fire the employees in the US office before you can fire the ones in the Berlin office.

2) Berlin in particular has a talent crunch, there aren't enough developers for the companies already there. Many of the top-tier developers are drawn to Frankfurt where the large companies are based (i.e where the money is). Many tech companies in Berlin resort to importing developers from elsewhere in the EU.