Remember when xkcd people used to talk like real people? I wonder what happened to those days. "Where have you been?" "Playing Half-Life 2" "Didn't that come out in 2004?" That's a real natural response - what's next? "What are you listening to?" "The Beatles?" "Didn't they break up in 1970?" People do play old games, you know. Is that so crazy?
I guess this comic is an example of what I've called Randall Munroe's Illustrated Picto-Blog - a place to write about ideas he has without the pressure of being funny. Not that this is a particularly interesting idea - but it's an even worse joke.
It doesn't stand up to even an iota of thought: The dude knows he is 5 years behind the times - so in 2013 he should know that everyone else has played Portal years ago. By spouting off the jokes, he isn't facing a "downside" to his idea so much as a "downside to him being fucking annoying."
In xkcd world, people look the same 5 years into the future as they do now.