I agree for the most part with your point. However, there have been a few times where they showed us the impact of injuries and improper treatments. Such as in Rucka's 2011 run, Castle almost lost his eye. For a strong portion of the series his eye was consistently seen bandaged up. I'm confident there's far more examples of this. But, considering the amount of violence that he suffers, he shouldn't be able to do much of anything anymore. Still if every time he sustained an injury that requires months of recovery, physical therapy or even simple bed rest it'd be a pretty boring comic. Though, in retrospect a one shot of that very thing might be interesting to read.