Someone had to go first. I would have expected some island to do it, like Isle of man. But why not Nevada. That does not mean that the lawmakers are particularly rational, just that they see a technology they like, or maybe they count it under good PR for the state.
Perhaps. Nevada went first because Google targeted it with lobbyists. I expect that the lobbyists did hit hard with the rational argument in favor of self-driving cars, that it will save hundreds or thousands or more lives compared to human drivers.
http://blogs.forbes.com/alexknapp/2011/06/22/nevada-passes-law-authorizing-driverless-cars/
http://news.ycombinator.com/item?id=2688424