In his book "Thinking Fast and Slow," Nobel-winning author Daniel Kahneman explains the phenomenon - not using Abe Darby as an example, of course. It seems we have a mental habit of throwing things into bins like "good" and "bad." If we absolutely love Abraham Darby's blooms and the fragrance of the rose, we may judge it "good." And at that point, unless we are "thinking slow" we begin to exclude "bad" characteristics from our mental model of it: it's a "good" rose, for gosh sakes. Of course, a large portion of the book is taken up explaining all the ways our judgment is compromised by our fast-thinking processes.

I participate in a rose forum. One week I'll rave about a rose. People will go "oooh aaaah." The next week I'll find something bad to say about that same rose. I'll say it out loud, and there will be total silence. The second bit of information is not consistent with the first, which established that the rose was "good." I think that's what happens, anyway. Maybe it has something to do with heresy.

At another level, I think your experience with Abe Darby may not be typical of rose growers across the US. The microclimate of coastal California is very different from the climate even thirty miles inland. Once you get to the other side of the Rockies, things change much more. Roses that do well from, say, Missouri north, east, and south tend to be ill-suited to much of California. And vice versa. I think the reputation that Abraham Darby has of good disease resistance might trace back to all those gardeners east of the Rockies whose rose gardens are completely leveled each year by blackspot - or would be if they grew the popular exhibition-winning hybrid teas popular on the west coast. Abe Darby was one of the first widely distributed roses that they could be successful with in about half a century. (I know this from having grown a hundred or so rose cultivars when I lived for a decade in NJ.) I have been told repeatedly by a rose gardener near Santa Rosa that it is impossible to grow roses in San Francisco because of the coolish weather and the fog. So even the cultivars bred on the west coast for west coast gardeners tend to fail where you live, I am told. If that is true, then your rust ridden Abe Darby might be well above average in terms of disease performance for roses in SF.