I actually haven't ever seen an apartment ad requiring debarking, but I have seen a lot for declawing.
I'll look for sources later when I have more time, but they have shown a definite link between declawing and changes in behavior, specifically no longer using litter boxes, spraying and biting. I mentioned craigslist because of the ads I've seen, where people admit to new problems after getting their cats declawed, either right in the ad or through emails I've exchanged with them. I got the animal shelter drop off rate from people who work there and have mentioned the high rate of declawed cats turned over because of behavior issues.
The point I'm trying to make is that a proportion of cats will develop spraying, litterbox or aggression* issues regardless. People who won't declaw because they think it's wrong are most likely (IMO) to also be more informed about environmental factors (placement and cleaning of litterboxes, avoiding things that stress a cat, etc.) that would minimize such behavios from occurring and would also be much less likely to get rid of a cat because of such behaviors. I've live with a lot of cats, and have seen no difference in the rate of incidence of behavior issues arising between declawed cats and those with claws.
I just don't think the correlation has been proven (and frankly, from what I have experienced, I would say it does not exist). I think that, in order to accurately draw such a correlation, you would have to study the incidence of problem behaviors in hooseholds with both declawed and nondeclawed cats. IMO, the human variable is by far the most important one, both in terms of the environment provided and the readiness to give up on a cat.
*I've never encountered a cat with aggression issues toward humans. IME, cats defend themselves when cornered or afraid, some cats lash out when overstimulated, and several of my cats will swat at me if I disturb them after they've gotten comfortable in my lap. I don't consider any of those "aggression issues" - they are normal cat behaviors. I think some people mess up by playing rough and tumble with kittens and puppies - that's something I have always avoided, because it tends to create problems down the road. For those who say that their cat attacks people out of nowhere, I would suspect that one could readily find reasons for that in early interactions between the cat and one or more humans.
Declawing is cruel and unnecessary. That, in and of itself, is more than enough reason not to do it.