Ya, I was 80% 'he's being sarcastic' and 20% 'uhhh...maybe not'
Anyhow outside vs inside gym - no argument there. I'm not blaming the gym for my knees at all.
As a kid, I used to play a real lot of indoor cricket...the best analogy I can give for non-Australians as to what that put my knees through is to think of a catcher in his crouch, and bouncing up for the throw to second base about 120 times in about 45 minutes, about 4 times a week. It messes with their knees over their careers, and it basically screwed mine for life in my formative years.
That said, the knees are generally OK day to day, get a bit sore when I run 10 miles or more, although in the warm climate I live in, don't cause me too much grief. Still, I do my best to not provoke them, and that's why I've steered clear of deadlifting for so long....still, I'm thinking the benefits may outweigh the risks and gonna give them a shot.