When IBM built the original PC, they let Microsoft keep the rights to the operating system software. In hindsight, it was a massive miscalculation as Microsoft's "software-without-the-hardware" business went on to earn more profits than IBM's hardware. IBM's later weak attempt with OS/2 to beat Windows failed.
Microsoft's then CTO Nathan Myhrvold (who Bill Gates considered one of the smartest guys on the planet) was on a phone call with Larry and Sergei and yelled into the phone that "Search is NOT A PRODUCT!!!". (Probably their MSN hubris speaking.) Microsoft's later attempt with Bing has hardly dented Google's search marketshare.
Google didn't notice the importance of social networking before Facebook did. Google's later attempt with Google+ Circles failed to trigger a mass exodus from Facebook.
Facebook.... <story is yet to be written> but the same thing will happen to them. Somebody will come up with something that blindsides them. Or it might not even sneak up on them. Mark Z himself may look at the early-stage product and conclude that it's not anything special.
There are plenty of untapped business ideas that Facebook will misjudge and dismiss, leaving others to win that market.
But to the author's point, it will suck if you create a product that paints a bullseye and it lines up in Facebook's crosshairs. Microsoft couldn't beat Intuit Quicken with MS Money but they did crush Netscape with IE. They lose some, they win some.