You're either intentionally dodging his point, or you're just dense. How is Kopitar likely to be less healthy going forward then RyJo? Because that was your statement he was responding to.
Here's an interesting study I found last year:
http://www.healthgeomatics.com/predicting-nhl-hockey-injuries/
In a nutshell, this guy's data crunching says that injuries are lower up to age 30, then increase after that. I would say it's definitely likely Kopitar would be less healthy overall, you can't fight age.
What Kopitar has going for him is that he has had relatively few injuries in his past, mostly small nagging ones and only the one big leg injury which doesn't appear to have slowed him down. He has a better chance of being healthy than most. RyJo, on the other hand, has had even fewer injuries, the big one being that weird thigh thing he had.
I don't think Kopitar is going to be on IR much even in his later years, but he's likely going to be on there more than RyJo is. Likely isn't a certainty, there's always outliers, but those are very uncommon.
It's a simplified analysis of injury data, but the trends apply to a lot of players - e.g. Gaborik, Crosby, Lupul, Hall, Malkin, Havlat, Letang, Lindros, etc. And those are just guys off the top of my head - high profile ones. It's not even counting the rank and file which should follow the same trend. Players who are injured a lot early in their careers tend to be injured a lot later. There are some outliers like Williams who had a lot of early injuries, but has been quite healthy since, but they are few and far between.
It's something that GM's don't appear to put much weight on, however. You can bet if Couture makes it to UFA in a couple years, he's going to get ridiculous offers, even though there is high confidence that he's going to miss huge chunks of games. I'd love to see a more detailed study done, wish I had the time to do it myself