Saying that "newyork.craigslist.org does not have any robots.txt and can be crawled as you like" is false. Search engines follow redirects until valid robots.txt files are found. From that same document you linked:
3xx (redirection)
Redirects will generally be followed until a valid result can be found (or a loop is recognized). We will follow a limited number of redirect hops (RFC 1945 for HTTP/1.0 allows up to 5 hops) and then stop and treat it as a 404. Handling of robots.txt redirects to disallowed URLs is undefined and discouraged. Handling of logical redirects for the robots.txt file based on HTML content that returns 2xx (frames, JavaScript, or meta refresh-type redirects) is undefined and discouraged.
3xx (redirection)
Redirects will generally be followed until a valid result can be found (or a loop is recognized). We will follow a limited number of redirect hops (RFC 1945 for HTTP/1.0 allows up to 5 hops) and then stop and treat it as a 404. Handling of robots.txt redirects to disallowed URLs is undefined and discouraged. Handling of logical redirects for the robots.txt file based on HTML content that returns 2xx (frames, JavaScript, or meta refresh-type redirects) is undefined and discouraged.