If you want to send a file from San Francisco to New York, the data will pass through a few different networks along the way, just as you would need to use multiple highways in order to drive from San Francisco to New York.
Interstate 80 goes from San Francisco to just outside New York. So aside from the last five miles (like the “last mile” problem?), you do NOT need to use multiple highways to get from SF to NY. Los Angeles would work. Wired has the right idea, but picked a bad example.
(Yes, I’m being pedantic. Remember, the Internet is not a big truck, it’s a series of tubes.)