Well, finance takes also a large chunk of Switzerland's GDP and thus is scooping up many engineers as well. Maybe it's not as pronounced as in London, but it certainly isn't very easy to hire good engineers here because of all the banks and hedge funds.

I think google came to Zurich because of EPFL/ETH, the very high living standard and most of all the rather liberal labor law. It's very easy to fire someone in Switzerland, compared to the surrounding countries.