[egor83]

A Dutch guy I know moved to Berlin to work on his startup there. We didn't discuss the reasons, but it seems Berlin has something better to offer.

If I start guessing - probably a better startup community. Amsterdam and Netherlands are corporation-friendly, with quite some big companies having headquarters there; but startups and corporations have different needs and make different communities.

UPDATE: Another point I can think of is the size of local market.

Maybe not too important for web startups that go global right away, but if you start locally (and thus use Dutch), you have 16M people in the Netherlands (+maybe 5 in the Dutch part of Belgium), while in Germany you get 82M, five times as much; plus another 8M in Austria and some more German speakers from Switzerland.