I suspect that the key reason Winston isn't derided for his absences the same way Carroll is essentially rests on the 'why' aspect, rather than the 'is' aspect of his injury problems. A chronic back injury (or even a fairly minor complaint) is something that is not only a problem in itself, but it impacts nearly every other part of the body. I won't labour over the details but when I was working as a nurse over 20 years ago, I tore 2 different muscles in my back at different times - and I simply couldn't do the job anymore physically; it wasn't just the debilitating pain in my back, but it affected my legs, my arms, my chest and stomach muscles - pretty much every bit of the body required to do a physically demanding job.
I get the impression that Winston is also the sort of player who will play through a pain barrier when needed, and whilst that's admirable, when one of the main reasons for your injury woes is based on a back injury, it won't ever get better, and you'll end up probably doing a massive amount of chronic damage not just to your back but possibly to your knees, ankles, shoulders and more. I think the analogy to Vincent Kompany is a decent one - the sort of player who will play through a pain barrier for the team's short-term gain but is something that is taking it's toll on him now (similar ages I think?).
We may have to be ruthless and let Winny go, and if so I wouldn't be too amazed if he retired not long afterwards - he's never gonna come back like he was (and for my money about 6 years ago he was one of the very best CB's in the whole PL).
This summer he'll have been with us 9 years - almost unheard of these days (aware AC's been here yonks too!) - and the sentimentalist in me would love to see him maybe get one more year and get a testimonial. He'll leave us with some fab memories and a few epic goal-scoring moments in our folklore forever.
And to be fair - I hope we can also remember those great Andy Carroll moments too.