Most of his work is done with his display. I just 'top up' his observations with screenshots on games he might not have seen. It's worth remembering that for various reasons I only tend to get games post-release, sometimes weeks after they've come out.
Very, very, VERY occasionally this can also lead to a re-evaluation of a resolution but the only one I can recall was Skate's 1080p mode on PS3.
In short, take nothing away from the man, like Wolverine, he's the best there is at what he does - and the fact he can be so precise from looking at an HDTV is absolutely remarkable.
EDIT: I'm currently watching my synchronised 720p feeds of Pure render out (yes it's Eurogamer face-off feature time again). What I said earlier in the thread about the minor screen tear differences remains, but the effects are identical. It's a pretty astonishing technical achievement bearing in mind how much stuff this game is throwing about. I never had that much respect for Climax as a developer, but this game is just an absolute delight.