Interesting, I would have still guessed Massachusetts due to the education system. If there goal is to make high paying jobs an educated population makes it much easier to find talent.
Amazon is already building a pretty big facility (about 5K employees as I recall). The upside is certainly the universities and the fact that Massachusetts is already a significant tech hub, albeit in a somewhat different vein from Silicon Valley. The downside is land and CoL in the city is very expensive and traffic/transit congestion is already pretty bad.