I think the original reason why getaddrinfo() has been designed to accept separate host and port args instead of a tuple is because the original C call does the same:
http://www2.research.att.com/~gsf/man/man3/getaddrinfo.html

Despite this apparently looks somewhat inconsistent with other calls like bind(), connect() and connect_ex() which take an address tuple, they reflect the original C behavior in the same manner, also because they're fundamentally different than getaddrinfo(), so I see no valid reason to change this situation.