He'll redirect the .co to the .net (as opposed to the .com to the .net).
But that doesn't help in the very (most?) common case of the users just typing .com and getting taken somewhere else entirely with no way for him to redirect them back. While it's true that many people will find their way to the site via search engines (rather than typing in the domain), the domain is likely going on things like business cards. And most people will just type .com on the end of whatever domain you tell them; they'll even type it when copying it off a business card that plainly says something else (and if it's ".co" pure muscle memory will add the "m").
Side Note: I wish they had of dropped the .com, .net, etc and just had the name. It only confuses users, why is whitehouse.gov different to whitehouse.com, whitehouse.net or whitehouse.com.au.
Well, then who gets to decide where a given domain points? Without TLDs, you would've had a situation where essentially the USA was the arbitrator who got to decide if (say) "Victoria" pointed to the website for a state in Australia, the capitol of British Columbia, a city in Minnesota, a lingerie company, or the personal website of Ms. David Beckham. Sure, that would've gotten worked out with "VictoriaBC" and "VictoriasSecret" etc, but would Australia be happy with the US (or US registrar companies) dictating how its government domains were named?